How can animals in the wild hunt during the night as if it were day? A remarkable biological feature acts as a pair of “natural” night vision goggles.

Animals can move and even hunt in the pitch-dark of the night. How do these animals see comfortably in the dark? How are their eyes different from ours?

Anatomically, the eye consists of three layers called the Tunica fibrosa (outer layer), the Tunica vasculosa (mid layer), and the Tunica nervosa (retina). The outer layer of the eye is composed of the sclera and cornea; the middle section of choroidea, corpus ciliare, and the iris; and the inner section of the retina.

Light rays reflected off objects first pass through the eye’s translucent layer (the cornea), then into the black round part located in the front of the eye (pupillae, or pupil), and later go through the lenses. The colored section around the pupil, covered by smooth muscles, is in charge of regulating the amount of light entering the eye. The real and inverted image of an object is projected on the retina by the refraction of light through the lens; the image is transmitted to the optical center of the brain as a result of nerve cell stimulation via the optical nerves. Sight happens as a result of these causal chains.

Now, there is a twist to all this: the optical center in the brain accepts spots that do not emit light as black. For humans, this means a loss of sight. Black objects are not visible because they absorb and keep all the light reaching them.

How could these animals, without night vision goggles, see in pitch blackness despite having the same optical mechanisms as humans?

The answer to this question was hidden in an anatomic structure (tapetum lucidum) located in the eyes of some vertebrates. This special structure, lacking in humans, monkeys, squirrels, birds, red kangaroos, and some other mammals, is found in equines, ruminants, and many carnivores. This structure is located in the cytoplasm of the choroidea layers in between the innermost light sensitive ocular layer and sclera, and it acts like a biological reflector. With its crystalline composition of varying colors from golden yellow to white, tapetum lucidum is a wonder of creation. The eyes of these animals shine when a light source is projected due to the aforementioned structure.

The primary task of this formation is to reflect the light which is projected to the rear section of the eye again without absorbing it. This happens due to the crystalline makeup. Thus, lower light levels are enhanced by the repeated reflection in the eye, and sight is enabled for animals. The second job of Tapetum lucidum is to elevate the sensitivity of the retina to light in order to transmit signals with no stimulation strength to the optical center.

This reminds us of night vision goggles. Night vision cameras are electro-optical devices that strengthen the light that is present. Light enters this device through the lens and hits the charged cathode, which has a lot of high energy. The energy load hits the phosphorous screen where the image is focused after passing through the vacuum inside the charger. The image is an enhanced picture on the phosphorous screen and it is not visible directly through the object. Tapetum lucidum however, is such an artistic work that it cannot even be compared with the night vision systems of technology. While the lifespan of a night vision system is only 2,500–4,000 hours (104–167 days), animals with Tapetum lucidum can benefit from this for a lifetime. The newest night vision systems, with a maximum optic range of 30-120 meters, cannot provide sight under light conditions one fourth of the moon’s illumination strength, whereas animals with Tapetum lucidum can see objects hundreds of meters away in much dimmer light.

This isn’t the only example of how masterfully and diverse eyes can be. Damseflies have over 30,000 simple eyes, called ommatids; eagles can see their prey from thousands of feet above them.

By the principle that “certain things are appreciated best in their absence,” if we imagine a dark night in which we are unable to see anything and cannot even step a foot safely, we can perhaps understand that Tapetum lucidum is a great blessing for these animals.

Reference

Veterinary Ophthalmology (2004) 7, 1,11–22. Comparative morphology of the tapetum lucidum (among selected species), F. J. Ollivier,* D. A. Samuelson, D. E. Brooks, P. A.Lewis, M. E. Kallberg and A. M. Komáromy.

Finally, I have come to say goodbye to you. As you probably know, there is a saying “Leave the best till last.” I am the greatest of all the organs and systems that have described themselves to you so far. I am an integrative system that forms a chain between every organ in your body. Just as your veins are spread out to carry nutrients and oxygen to every part of your body, I also embrace your entire system like a network, without leaving the tiniest space; I am informed of everything that goes on inside your body. Even if a tiny insect settles on your arm, you sense it immediately. I make you aware of a tiny drop of sweat on your body. I induce pain in suitable measures to inform you of any illnesses in your inner organs. In fact, I not only inform you, I also warn you to seek help.

However, it is hard for me to describe myself. When you hear the words “nervous system,” what comes to mind is a cluster of cells called neurons. But this is a great mass of cells, and we should always remember that we are referring to the most complex matter in all of creation. The very important main nervous systems, which are very close to one another, are the huge masses positioned beneath the skull, the extensions of my system and secondary nervous system; this latter is spread out through various regions of the body. It would take up too much of your time to describe each region and branch of my system individually to you each month, but in this way I could prove what a perfect and incredible duty each of them performs within your body. However, I will try to explain the subject briefly to avoid boring you. Nevertheless, please forgive me if I ramble on too much; we are describing the most excellent organ created by God so it is inevitable that there will be some complicated matters that need clarification.

Instead of allowing each of my sections to describe themselves to you individually, I will speak on their behalf as the “brain.” It may be easier for you to understand the system if we divide it into two. One of them is me and the nervous system which I lead; we can briefly describe this as the thalamus, hypothalamus, cerebellum, the medulla, and the spine. The other part is the peripheral nervous system, which emerges from the central nervous system and is distributed, rather like fiber optic telephone cables, throughout the entire body. In addition to me, the brain, and my two large cerebral hemispheres, there is another smaller section, which is known as the brain stem. The brain and its cerebral hemispheres and the sections of the brain stem which are protected beneath the skull (the cerebellum, medulla, thalamus, and hypothalamus) are very important. The spinal cord, which is also a part of the central nervous system, however is not in the skull, but positioned within the vertebrae that constitute the spine. Due to its connection with the central nervous system, any damage to the spinal cord can endanger life.

Although damage to regions of the body where the nerves are distributed from the central nervous system may cause paralysis, or functional disorder for the specific organ, such an incident is not life threatening.

If you recall, when the heart and circulation system described themselves they boasted – indeed the veins also seemed to brag a bit when they stated that they measured 75,000 miles (long enough to go around the world almost three times). But the nerves are approximately 477,000 miles, long enough to stretch from the earth to the moon, and back again… the nerves which are distributed throughout the various parts of your body measure 250,000 miles, and the total length of the central nervous system is 228,000 miles. Almost 200,000 signals pass through just one cell at a time, which means that every moment thousands of signals pass through millions of my cells all throughout your body, and flow from the central nervous system to the whole body and then back to the central nervous system. There are about 30 billion cells in my system. 10 billion of these cells are in the cortex, 10 billion in the cerebellum, and the remainder forms the structure of the nerves and other sections. As a comparison, a fly’s brain contains 100 thousand cells, and a rat’s brain has 10 million cells. The total number of connections and contact points (synapses) that my 30 billion cells use to send and receive signals is 100 trillion. The number of combinations that these connections can establish to send signals to one another is greater than the number of atoms in the universe. At the beginning of a thinking process, the number of cells activated is between 10 and 100 million, and according to the depth and intensity of the activity, these figures can increase to astounding numbers. Every second 4 billion signals are exchanged between the left and right hemispheres. When you were an embryo, just a few weeks old, I consisted of 92% water. When you were first born, the ratio of water was 90%. And when you were fully developed, the water ratio remains at 77%. Peter! Can you imagine, a heap of mass consisting of 77% water, the remainder made up of various element. Our Lord, the bearer of eternal power places me in you, in the head of the most honorable creation, and with me you form civilizations; you invent and discover. And even more important, with my mediation you have the ability to contemplate and reach your Creator. What we are learning about here is how with me you are able to recognize the wisdom of the entire universe. The electric signals of the various sense organs, such as the eyes, ears, nose, tongue and skin, all of which have previously described themselves, are transmitted by the receptive cells on various wavelengths; these are then conveyed to you in the form of sight, noise, smell and taste. In fact I am inducing you to write these words at this very moment. The evaluation of everything you do passes through me, but you are not even aware of it. When you walk, eat, talk, speak or sleep, the information I receive from every part of your body is reviewed and responded to in a suitable manner. Dear Peter! Could a single nucleus of a single one of my cells possibly position itself alone?

The Lord has created me so magnificently that you are still only aware of a very few of my mysteries. Each of the sections that I mentioned above has a distinct and important vital function. On their behalf, I will briefly explain their duties: The cerebellum is the nerve center from which the harmony of balance and muscle movement is controlled. As this section of me has no sense of perception, it is impossible to voluntarily change the functions of this region. The pyramid shaped medulla oblongata, which connects the spinal cord to the midbrain and the pons; the latter constitutes the other end of the brainstem through a hole in the back of the skull in the form of the spinal cord and enters into the vertebral column. Here, there are many nerve centers which regulate autonomic nervous system activity, such as the heart rate, breathing, and digestion process. This is also the center from which the reflexes are controlled, the body’s inner environment is regulated, and this center, working with the cerebellum also controls movement and coordinates signals received from the nerves of inner organs. Moreover, activities such as excitement and sleep are also controlled here in collaboration with the thalamus.

The thalamus lies between the brainstem and the hemispheres of the brain, performing a function rather like a junction or relay station. This section gathers all the signals sent by the sense receptors, except for those from the olfactory (smell) receptors, and conveys these signals to the cortex reflecting the information; there is also a role played in consciously identifying sensations such as pain, touch and noise. There is also a role played in the sensory changes that occur with the perception of senses in our consciousness and awareness, as well as in the regulation of sleep and paying attention. The hypothalamus, which is located below the thalamus, is an important center that controls sexual senses; the sensations of pain, pleasure, hunger, and thirst, as well as blood pressure, temperature and other functions of the inner organs. It also performs the important duty of regulating hormone release. The nerve fibers that enter this center, which is the location of a very complex network of nerves coming from the olfactory bulb, thalamus, and the frontal lobe, reach the autonomic nervous system, the reticular formation in the stem section, and the posterior lobe behind the pituitary gland (hypophysis). The pituitary gland, one of the most important systems that earlier described itself in the endocrine system, produces hormones that stimulate secretion in the anterior section, as well as the oxytocin and antidiuretic hormones which are stored and released from the posterior pituitary.

On the base of the deep grove that separates the two hemispheres of the large brain there is a callus-like body; this is a bundle of axon (nerves) called the corpus callosum which connects the two hemispheres. Because the nerve fibers cross and change direction in the medulla, the left side of the brain controls your right side, and the right controls your left. Although my two hemispheres may look like a reflection of one another, there are some variations in their duties; for example, the left hemisphere controls speech, but the section which controls the perception of location is in the right hemisphere. Whilst you use the left hemisphere for duties that must be performed in a specific order (activities such as adding and subtracting or buttoning a shirt), you use the right hemisphere in thinking with images (for example, mapping the route from your home to the market). If the callus substance that connects my two hemispheres did not exist, there would be no communication between the two, therefore, you could read the word “fish,” but you would not be able to picture the image of a fish in your mind without the right hemisphere to achieve this.

The brain, the grey-colored mass of folds and grooves that covers the top of my anatomic hemispheres, the region where the main stems of my cells are found, is called the cortex or grey matter; the lighter colored matter that lies beneath this, the region where the axons (stems of neurons) are found, is called the white matter. My cortex region, which is composed of six layers of cells, is the center where the sensory signals are received and analyzed and where voluntary muscle movement is controlled, while also being the center of activities, such as learning, reasoning, and remembering. My two hemispheres, the focal point of conscious activity and thought that forms the large brain, constitute 85% of the whole brain. When you were first born I weighed 400 grams, but I grew very quickly, and by the time you were a year old I weighed 800 grams. When you were four years old, I weighed 1,200 gr. However, my growth began to slow down after the age of seven, and when you reach twenty, I will weigh approximately 1,379–1,434 grams. When you begin to pass your first youth, my weight begins to decrease every year by 1 gram, so when you reach seventy-five, I would have shrunk in comparison to when you were twenty. The reason for this decrease in weight is that approximate 50,000 neurons die, or cease to function daily, after you reach the age of twenty. The body cells of the cartilage, bone, skin, ligaments and the liver divide, regenerate and increase in number; however, the nerve cells that are part of me continue to increase until they reach the figure set out for you when you were formed in your mother’s womb; they then lose the ability to segregate. So if there is any damage, relative functions fail because the cells in that region have died. Then the question arises: As there is no increase in the numbers of cells, how does the weight continue to increase until the age of twenty? Well, there is not an increase in the numbers of cells; rather, there is an increase in the number and growth of connections between the cells and this is how my weight increases. Of course, nutrients are added to build and stimulate these connections. Subsequently, with age these connections begin to decrease. With ever experience you have, all the things that you learn or see during your youth these connections increase, and in turn this increases my capacity for thought and reasoning. If you continue to activate your brain by reading, writing and other social activities in old age, these connections continue to increase. Even if there is a decrease in my cells, you are able to continue your usual activities without losing any functions of the brain. But as soon as you say that is enough, it is time for a rest, my cells begin to withdraw their connections immediately, and in time you will certainly see the difference in my capacity. If the cells in my central nervous system are injured or damaged, they cannot repair themselves. However, if the cell bodies of my cells in the peripheral nervous system are not damaged the stems are repairable.

Thanks to this special feature if a severed arm, leg or finger can be carefully replaced with microsurgery, the nerves can repair themselves, and the limb will continue its normal functions. The visible cause of this characteristic is found in the nerves of the arms and legs, but not in the brain or spine, is the casing that surrounds this bundle of nerves that transmits signals for the cells to grow. Even with the greatest of techniques, no surgeon could sew the severed nerve fibers. However, thanks to the nerve casing that holds these fibers together (like the plastic that covers the electric cable, consisting of thin wires) the severed limb can be replanted. Then with guidance from this outer casing, each of the hundreds of fibers found inside grow 1 mm every day, and in a period of between 1 month and a year, they will begin to function again.

Irfan Yilmaz is a professor of biology at Dokuz Eylul University, Izmir. 

I, the protective system that you call the “immune system,” am divided into different groups and sections, each of which has its own area of expertise. Just like a military unit, each of my groups has to be partially or fully trained before it begins life in my system so that it can properly fulfill its defensive function. “Soldiers” in this protective troop work according to what expertise they have and the type of “enemy” (alien microorganisms) they encounter. Some are equipped with heavy weapons against tough enemies; some produce a special poison with which they kill their enemies by injecting it into their bodies, some work like a waste disposal, smashing up the dead bodies of the enemies, and some of them eat the alien intruders alive when they attack your body. Others produce raw material to arm your body, some turn that material into weapons, some work as defenders, some are signalers, some are rangers and some are equipped with a special intelligence which allows them to recognize the previous invaders and destroy them more easily at their future encounter. In this intelligence system, which works like an information center, the soldiers check the dangerous invaders and remember their previous experience with them. Then, they develop a strategy to fight against those invaders. If the enemy is known well, the defense against it will be easier.

Now, using this analogy, I will talk about your enemies and the features of my soldiers that are placed in your body to fight against them. However, I have to remind you of something first: as you know, every army has to have a top commander. Similarly, there is someone who has placed such a perfect system like me in your body, someone who has boundless knowledge and power, and has no one else superior to Him or has no one to receive orders and instructions. That is our Lord God Almighty. Since He knows very well what kinds of enemies you will face, He has created me with all my troops so that you can be defended against those enemies.

The enemies of your body are germs, which enter your body through different passage ways, including digestion, respiration, excretion and the skin. “Germ” is a general term referring to many kinds of micro-organisms. Some of them are bacteria, some are fungi and some are viruses. Your body needs different special tactics to defend against each group of germs and my soldiers are quite talented in those tactics. I have to be always watchful against germs coming from outside. Not only that, but I also have to be careful about inner enemies, that is, the cells in your body which suddenly turn into “terrorists” becoming harmful and spoiling the system. You call those cells “cancerous.” It is a great challenge for me to cope with those cells because they originate from among your very own cells and they know our tactics very well. Nevertheless, with God’s help, we can defeat them. However, when too much stress and anxiety weaken me I might miss some of those cancerous cells, which will grow and become tumors. In fact, cancerous cells develop much more in number than is commonly known. But my soldiers constantly check every single cell that is formed in your body and try to see whether it is normal or not. As soon as they discover a cancerous “terrorist” cell, they try to quickly destroy it. However, some cancerous cells are disguised like a wolf wearing a sheepskin so that they can avoid detection. My soldiers make rounds and check the cells from outside by only looking at their skin. Thus, they can be manipulated. All of your cells, including those with germs or cancer, contain protein with a special code which identifies the cells as being yours. When my soldiers encounter our fellow cells carrying those coded proteins, they release them. But the enemies who do not carry this code (or password) are immediately caught and destroyed. When we have diseases like cancer, however, the cancerous cells may evade our “rounds man” because they know this password. Sometimes the opposite may happen: my soldiers get confused and cannot identify their fellow cells despite carrying the right password, assume that they are enemies and start to attack them. These types of diseases, called Autoimmune diseases, emerge with a quite complicated mechanism which is a puzzle even for me! For example, during rheumatoid arthritis, which is among the many long-lasting and unrecoverable diseases, my soldiers attack and gradually destroy the tissues like cartilage, cardiac muscle, eye lenses, and the tubes of the kidneys with which they share a body. In fact, when we are created as a whole system (when you are only an embryo in your mother’s womb), some of my soldiers make an agreement with the other cells of your body, announcing that they will forever stay friends with them, will show tolerance to them and will only attack the enemies. But, somehow this agreement is broken later; my soldiers do not obey me anymore.

Now it is time for my group of soldiers to introduce themselves:

The most general term by which we are identified with is white blood cells or leukocyte. We appear approximately 6,000 to 7,000 times in each cubic millimeter of human blood. The other blood cells, which are called red blood cells (erythrocyte) are red in color; it is for this reason that we are called white. Since blood vessels can reach to the remotest edges of the body, we roam around the body through those vessels and look for work to do. Of course, not everyone can do everything. So, we are first divided into two sections. The cells in the first section contain microscopic granules, so they are called granular leukocyte. The cells in the second section do not contain such granules, so they are called agranular leukocyte. Those sections are divided into groups among themselves. The first section has three groups: neutrophils, eosinophils and basophils. The second section has two groups named monocyte and lymphocyte.

Eosinophills: You may not know much about these soldiers that make up 12% of the whole protective body. However, during allergic reactions and diseases caused by parasites, the number of these soldiers increases. They complete the effect of the antibodies produced against the antigens. Some chemical substances like histamine appear as a reaction to antigens, such as itchiness, rash, and swelling. Eosinophils reduce the effects of those substances and the symptoms.

Basophils, which are the least in number, make up the 0.5% of the body. Those soldiers are present mostly in the scars that are healing or in highly infected areas. The granules inside basophils contain two very important substances called heparin and histamine. Histamine helps expand the blood vessels and accelerates the release of active substances within me from the blood vessel walls, enabling them to reach to the affected area. Heparin also prevents the blockage of blood vessels because of blood clot.

Lymphocytes of the second section are the group of soldiers which goes through special training and has expertise in many subjects. They make up 20-25% of the soldiers in my system. Those soldiers detect antigens and germs and remove them from the body. Every soldier has a detector which identifies a certain antigen. Therefore, in your blood, there are millions of lymphocyte soldiers, which are different from each other and do not have a pair. For any antigen of a germ, you will definitely find a lymphocyte that finds and kills it. Those soldiers can be grouped according to their appearances, as small, medium, and large lymphocytes. Each group has different special features. We can also divide them according to their maturation and training process as B-lymphocytes and T-lymphocytes. Although both of them originate from stem cells in the bone marrow, T-lymphocytes mature in the thymus before they move to the other lymph tissues such as the spleen, liver, and tonsils (Thymus is a gland in the chest that talked about itself in the previous issue). B-lymphocytes, however, mature in the bone marrow, and go directly to the tonsils, appendicitis, spleen and other lymph tissues. When the T lymphocytes mature in the bone marrow, they acquire different new features. Some of them work as T helper cell, some work as natural killer T-cells and some work as suppressor T-cell. A helper T-cell, which is triggered by an antigen that is specific to it, secretes lymphokines, which makes B-cells produce antibodies. Among those lymphokines, interleukin-2 activates the natural killer T-cells, which kill the infected cells. The killer T-cells do not bind directly to an antigen. Rather, they secrete a substance that kills the infected cell after joining with the antibodies that were previously bound to the infected cells. On average, T-cells live 2-4 years; some, however, live more than 10 years. Today, the defense mechanism of the T-lymphocytes creates an issue in terms of organ transplantation. If, for some reason, a foreign organ (a kidney or heart, for example) is transplanted into the body, the T-lymphocytes attack that organ immediately. Those “headless” soldiers do not know that the body really needs that organ and try to eliminate it, therefore, leading to transplant rejection or tissue incompatibility. The T-lymphocytes treat the foreign organ the same way as they do to the cancerous cells: they attack and try to destroy it. For this reason, the immunologists are trying to discover medicines that will help them control the soldier T-lymphocytes whenever they need to be stopped.

Dear Peter, have you ever thought about how all this happens? While you have no idea about a germ that might enter your body, those memory cells, which are placed in your blood with a boundless compassion by our Creator, remember an enemy that they saw years ago, and begin to make weapons right away. Since those cells are devoid of reason and consciousness, to operate them there has to be Someone with a great knowledge and will.

The lymph nodes are production centers for the lymphocytes found at some particular places in the body. They resemble variously sized military headquarters. The lymphocytes are produced mostly at infection sites, which are the little lymph tissue groups located under the epithelium that lines along the walls of the digestive tube, respiratory track, and the bladder. When fighting with bacterial infections the lymph nodes swell and enlarge as much as 1–2 cm. In addition to the lymph nodes that extend through the lymph vessels, the areas such as nape, groin and the axilla (underarm) also contain lymph nodes. If you get an upper respiratory tract infection, the lymph nodes at your tonsils and neck areas become swollen. If you get a urinary track infection the nodes in your groin area become swollen. As for digestive track infections, it is the responsibility of the lymphocytes in your appendix to fight against germs. Some scientists view this organ, which is an extension of the cecum (the blind gut), as a “dead” piece of intestine. Both the appendix and tonsils are quite useful organs that produce lymphocytes in normal circumstances; they are not some useless remnants. For that reason, it is not right to remove them when it is not really necessary. However, we have to remember the proverb that says, “We salt the food so that it does not smell bad; but, what do we do if the salt itself smells bad? Then, we have to get rid of the salt.” Similarly, in some bodies where my system is weak and so is lymphocyte production, those areas become home to germs and you have to remove them.

Other than the soldiers of the immune system, several organs in your body have their own ways of protecting your body. Those organs do not have soldiers like in my system; theirs are like a “civil defense.” Chief among those are your skin which works as a natural barricade against the entrance of the germs, the mucous membrane that lines along the walls of your mouth and inner nose, interferon which is a substance produced by your cells against viruses, and an antibacterial substance called lysozyme which exists in your tears and sweat. Therefore, sweating, crying, and runny nose are not things to be ashamed of; they are only the protective systems that have been naturally placed in your body by our Lord God.

Dear Peter, I think I should stop here although there are still so many features of me that you have to discover. After all, beneath all diseases and deaths you will find disorders related to me. The biochemical processes in which many of my soldiers operate are not exactly known yet. If those are revealed, doctors will likely succeed in healing many other diseases. However, sooner or later you will reach the destined end: death. No creation can be immortal; there will definitely be a problem and you will have to leave this world, wherein you are only a guest. If you carefully contemplate the works of art in your body, in the hereafter you will have solved the riddle of the delicacies of those works. Of course, everyone’s time of death is unknown. Therefore, in this limited time, give your organs their due and give thanks to the God Almighty who gave you those gifts. Live according to His will, and always remember to glorify Him. Goodbye, Peter! May you and your troop be healthy!

Irfan Yilmaz is a professor of biology at Dokuz Eylul University, Izmir, Turkey

Dear Peter, in order for you to understand me better, keep in mind a basic principle about the functioning of living organisms-they all depend on energy use. If no energy enters a living system, then no metabolic activity, no life function can be carried out. Think about a car without fuel. No matter how great the car is, it simply won’t work without any fuel in the tank. The human body is no different. Plants and animal products which people consume as food provide the body with fuel. However, you cannot make use of the energy in nutrients in the form in which you take them in. They need to undergo a process so that they become usable fuel for us, like crude oil being refined into gasoline to make a car work. This is roughly what my duty is. Without my functioning, you would be devoid of the energy to move a finger, and eventually die. Do you understand now how important a set of pipes I am? You just think that I look like a soft and hollow canal and misjudge me as simple. Well, I know that I don’t have such complex parts as the heart, lungs, and kidneys, but I’m created as a perfect work of art in plain design.

Although the hoses you use for watering your garden wear out and break in a relatively short time, my walls made of four layers keep functioning through a lifetime without any holes unless I contract a disease like cancer. My outer layer consists of a durable connective tissue, the next one consists of two sets-one horizontally and one vertically laid-of straight muscles, the next layer under that consists of glands spread in a soft connective tissue, and the innermost layer is the epithelial mucosa where the actual absorption takes place.

Now, let’s come to how I achieve digestion, one of your body’s vital activities. Actually, there is no place for me to take any pride in it; I’m just doing as I am ordered. Anyway, the complex processes occurring within my simple-looking walls are just fascinating! Every one of my cells producing the particular enzymes to break up each nutrient is like a separate factory. Some of these enzymes break proteins into different levels of peptides, some break the peptides into amino acids, some break fats into fat acids and glycerin, whereas some break carbohydrates down into glucose. All of these particular enzymes have their sub-branches within themselves. For example the enzymes breaking down fructose (fruit sugar), lactose (milk sugar), and starch are all different. In order for the enzymes to be effective, my inside needs to have the right pH level; the enzymes work in very sensitive conditions. To give you an idea, the enzymes in the stomach-which happens to be the second station the nutrients are destined for before they come to me-work in an acidic environment (pH: 2.5–3). In my case however, basic fluids are secreted and this strong acidity is neutralized for my enzymes to work.

My overall length is around 8.5 meters from the first entrance at the stomach to the last exit. The small intestine is nearly 7 meters long and the remaining 1.5-meter section is the large intestine. Although the small intestine is the longest section of the digestive tract, it is still called small since it is smaller in diameter than the large intestine.

The small intestine is also divided into three sections. The very short (25–30cm) and relatively thicker part right after the stomach is the duodenum. Bile-which works like detergent and facilitates breaking up fats-produced by the liver and digestive enzymes from the pancreas enter the duodenum. Thus, the nutrients are digested one step further and pass on to the second section (jejunum) and then to the third (ileum). You cannot easily tell apart these final two sections. As blood circulation is more intense in the second section, this section is more reddish and the contractions here are faster and stronger. The third section is narrower and has thinner walls. The blood circulation here is relatively lower and the movements are more limited. The thin membrane of connective tissue (mesentery) around me which attaches me to the abdomen wall and prevents me from knotting up is relatively fatty in this third section.

My most vital parts are the villi-tiny nipples covering the curly surface of my inner wall like a carpet. Shaped like the fingers of a glove, villi yield an enormously large inner surface. They contain a net of capillaries and lymph canals. In addition to the glands secreting the enzymes to break down nutrients, the secretion of certain glands protects me against the destructive effect of the stomach acid. Some cells secrete mucus for lubrication and protection of the passing nutrients. As some cells of the villi secrete digestive enzymes, some of my cells absorb the nutrients broken down until the final phase and pass them to the bloodstream.

Peter, how can some guys mistake such a splendid mechanism as a work of unconscious nature? What I’m telling you about is a manifestation of such great knowledge and might that it leaves you spellbound. I know the characteristics of foods, I know about the other organs’ needs, I adjust various enzymes and an absorption system, I fit them in a limited space… In addition, I do all these in the most ideal way, without any waste or flaw! C’mon Peter, can all these happen by themselves? Now, if I were to start telling everyone about the absorption mechanism in detail, they would probably see those cells as divine beings! The One who assigned special carrier molecules and a system for every nutrient molecule, has placed two transfer systems as blood and lymph pathways in every single one of those millions of villi! The blood pathway passes amino acids, water and salts into the blood directly, whereas the lymphatic pathway absorbs fats to pass them to the blood indirectly. After absorption, the nutrients become a property of the body and they are carried in the bloodstream to all the cells waiting for them in need.

Well, what about the waste then? Since everything you eat is not beneficial and usable, and some things are even toxic, they should be disposed of as soon as possible. The unabsorbed remnants are still too watery to be disposed of; sending them away as they are will be a waste of water and minerals. But don’t worry, everything is perfectly planned! Now the large intestine comes on duty. In this 1.5-meter section, the water of the waste and certain minerals are absorbed, and the waste solidifies. The large intestine is also divided into three sub-sections. The pouch connected to the junction of the small and large intestines is named the cecum and there’s the appendix at its end. This end sometimes festers and you have to have it removed in an appendectomy. Now, there’s this made-up story that the appendix was once longer since your ancestors only ate plants, that it has evolved into a shorter form for I now eat more meat, so on and so forth… Bah! Nothing is created in vain, Peter. If it didn’t have a duty, it simply wouldn’t be created. Only after some time did it dawn on them, after researchers proved that it is so necessary, that as a lymphoid organ, rich in blood vessels, it produces antibodies to fight the germs which somehow make their way into me.

The rest of the large intestine is the colon and the rectum. The mucosa covering my inner surface is rather smooth. It secretes mucus to facilitate the removal of waste. In addition, useful bacteria are made to work in abundance in the large intestine for your needs. These bacteria synthesize the group B vitamins like B12, thiamin, and riboflavin, along with vitamin K. You see how all the processes are carried out so splendidly? If it weren’t for vitamin K, your blood would fail to coagulate, and the slightest injury to your blood vessels would kill you. Could you ever have imagined that what looks to you like a sewage canal could produce vitamins of vital significance? Your Creator has infinite wisdom.

Peter, now you may wonder how the acts of this organ which resembles a long hose are regulated, how the nutrients inside are propelled, and then thrown out. To put it briefly, the “willful” part of your brain does not even know about it. Indeed, if it knew, it would be constantly busy with me and unable to do anything else.

Under the control of the autonomous nervous system, the straight muscles of my walls gradually contract in waves-this is squeezing act is called peristalsis. The nerve fibers connected to me fall into two basic categories-sympathetic and parasympathetic. As the sympathetic fibers pressure me to slow down, parasympathetic fibers stimulate me to act. Thus, I try to keep a balanced functioning between these two opposite effects. When the waste material I propel this way assumes a state to be disposed of, it reaches the rectum, and when the walls here strain, I make a natural call to you that I need to get rid of garbage. This is the step where your will has a partial interference.

Colon cancer, which troubles many people today, appears in this final section. The major reason is consuming too much meat and fatty foods, lack of movement, and leading a stressful life. When these are combined, I fail to function properly. If you want to help me at that, you should consume fiber-rich foods such as fruit and vegetables, and also lead a peaceful life. My web of nerves is amazingly rich and complex. Therefore, I am sensitive to nervous changes. If you feel down or sad, and if you suffer too much stress, I begin to go into spasms. Then I fail to dispose of waste, the toxic material inside me begins to damage my inner walls and eventually increases your cancer risk. Therefore, you’d better take up the habit of a glass of warm water when you get up in the morning, and try to have regular meals at the same times of the day. Most importantly, always have fresh green vegetables on your table, reduce meat intake… and it would be great if you could afford to consume olive oil rather than any other.

Hey, wait! I was about to forget the most important point. If you don’t have any peace of mind, all of these will be useless. This doesn’t mean that you will never worry; after all, this world is a testing ground and you are a human being like anyone else. However, if you give in to troubles and get overcome by feelings like panic, fatigue, and hopelessness, then my functioning will be upset. So, troubles faced with active patience and effort without giving up hope do not harm me much.

Peter, I do not wish you to wait until you see colon cancer patients disposing of waste through a hole in their belly into a plastic bag before you feel grateful for the blessings you enjoy. Actually, maybe I have told you at most a tenth of what I know about myself. Anyway, I think even this much will give you an idea of what a work of art I am. Thanks for listening to me, Peter!

Irfan Yilmaz is a professor of biology at Dokuz Eylül University, Izmir, Turkey.

The tradition of our scientific and technological explosion continues in the new millennium as an inheritance from the nineteenth and twentieth centuries. The need to publicize scientific developments has caused Web publishers to prepare a site to announce daily science news. It is updated three times a day. The following scientific disciplines are covered:

•Health & Medicine, Cells & Microbes, Mind & Brain, Plants & Animals are located in the Life Sciences section.

•Space & Time, Matter & Energy, Earth & Climate, Computers & Math are subdepartments of the Physical Sciences section.

•Engineering & Tech, Fossils & Ruins, Fun & Learning, and Trends & Issues are subdepartments of the Science & Society section.

•The “picture of the day” is published in the Image Gallery section. Images are being archieved in this section and categorized according to topic. Top-rated images also are listed here.

•Newsgroups on scientific subjects are located in the Discussion section. Topics for the “talk of the day” for the news-groups and the message archive can be found, too.

Hubble thing

http://oposite.stsci.edu is the Web address of the Space Telescope Science Institute (STSCI), a site operated for NASA. The Latest News from Hubble and Hubble Pictures are published by this page.

•All pictures since 1990 are being archived in the Gallery section. The Gallery of Planetary Nebulae contains more than 100 pictures.

•The Education section contains subdepartments of Education at Hubble and Origins: Searching for Our Cosmic Roots.

•The Sci-Tech section covers The Story of the Hubble Space Telescope and features a tour of the STSCI facility.

Family and Health

The virtual version of the American Academy of Family Physicians is located at www.aafp.org. Its main topics are family health and nutrition. Visitors are asked a daily question.

• The Family Practice section contains definitions, statistics, and government and advocacy information.

• The Clinical Information section features information on family health policies and research. CME (Continuing Medical Education) and lists courses, calendars, and on-line credit departments. This latter information is especially helpful for students who want to continue their medical education.

Journals, directories, and newsletters about family health are located in the Publications section.

AAFP also publishes www.familydoctor.org.