Читать книгу The Body at Work: A Treatise on the Principles of Physiology онлайн

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Bacteria are the world’s scavengers. To them ultimately belongs the task of reducing organic matter to the salts which plants reorganize. The cycle of life would be broken if bacteria were suppressed. No sooner has an animal fallen than these little agents commence their beneficent task of resolving its carcass into air and soil. Birds and insects may interrupt their work. They may steal portions of the derelict, use them for fuel, or patch them between their own ribs. But they, too, will soon lie breathless on the ground; and the bacteria are always ready to finish their interrupted task. Why should they wait until the slight change occurs, important to us, but of little consequence to them, which marks the transition of living protoplasm into dead proteins? There is nothing in the constitution of protoplasm which makes it harder to break up than protein. There is no quality inherent in living matter which makes it resistant of decay. We resent the officiousness which prompts bacteria to obtain entrance into the ship while it is still under full sail, with a view to commencing the work of demolition. Deep in our minds lies the conviction that it is contrary to the rules of Nature. We are especially annoyed at the many ruses bacteria adopt to disguise their personalities. The bacteria of the soil we can keep at a proper distance. But bacteria of the stream, bacteria of milk, bacteria of the breath that would betray us with a kiss! It is hard to recognize that they are fairly and squarely playing their part. Birds and insects we can beat off with our hands. Our invisible enemies are everywhere. They are constantly insinuating themselves through scratches in the skin, through abrasions in the mouth, through surfaces of the intestine left unprotected owing to the desquamation of its epithelium. But if we are constantly open to attack, we are policed by myriads of zealous leucocytes, ever ready to reduce the invaders to impotence. The germs which have found entrance fire off a toxin. The leucocytes reply with an antitoxin. There is absolutely no limit to the power of protoplasm to protect itself, if only it be not taken by surprise. It can resist any organic poison if it is allowed a sufficient time to produce the antipoison. The ferment of pancreatic juice, trypsin, is a poison which is unlikely to find its way into the blood. When injected it produces disastrous results owing to its immense activity in digesting proteins. An animal “prepared” by the injection of successive doses of trypsin develops an antitrypsin. Injection of pancreatic juice no longer does it any harm. Tapeworms which live in the intestines are bathed in pancreatic juice; they are constantly exposed to its digestive action. They are not digested, because they secrete an antibody which prevents the development of the activity of trypsin. It is not in this case, strictly speaking, antitrypsin. It is antikinase, a substance which, if extracted from the bodies of tapeworms and added to pancreatic juice, renders it incapable of digesting albumin. The antikinase does not destroy trypsin, but destroys kinase, the co-operation of which is essential to its activity.