Many more instances might be cited of this capacity of developing “antibodies” of protoplasm. The leucocytes of the blood are incessantly adapting their chemistry to the needs of the economy. All the tissues, it may be supposed, possess the power of developing resistant ferments; but the leucocytes ([Fig. 4]) are the undifferentiated cells, the maids-of-all-work. They have not specialized as makers of ptyalin or makers of pepsin. They are not completely given up to lifting weights, like muscles, or carrying messages, like nerves.
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.
Not only has protoplasm the power of meeting with an antiferment any ferment which might prove prejudicial to its own integrity; but after it has been once attacked it continues to defend the vulnerable spot. Its tactics are, it must be confessed, somewhat like those of the dusky warrior who, during his first lessons in the art of boxing, made a point of covering with his fist the place where he had just been hit; but even its power of remembering its last injury is of supreme value to the human race. Before the age of sanitary science, and even, in certain backward communities, in these days of its beneficent rule, conditions producing disease were not necessarily set right as soon as the epidemic was over. The close-packed inhabitants of a ghetto were continuously exposed to germs of typhoid fever, small-pox, whooping-cough. But after their protoplasm had once responded to the need for the production of an antigerm, it either continued for many years to keep a stock in hand, or it kept the recipe within easy reach. The memory of protoplasm is amazing. It is commonly said that vaccination is an absolute protection for seven years. There is no doubt but that the immunity from small-pox which it induces, if gradually lessening, lasts for life. The disease, if it attacks a person who has been vaccinated in infancy, is relatively harmless.
Inoculation, vaccination, is the boxing-master’s method of utilizing the self-protective instinct of the dusky warrior. Knowing that his pupil will for a long while continue to cover an injured spot, he asks himself: “Where is he most likely, when it comes to a serious contest, to be hit?” Then he gives him a gentle tap in that particular place. Does he need to know how to defend himself against small-pox? Give him cow-pox. Is he likely to receive a knock-down blow from typhoid fever? Just show him what it feels like to have a gentle shake. Educate his protoplasm to make antityphoid ferment, by giving him the typhoid germ in such an attenuated form that it cannot do him any harm.
The chemistry of protoplasm is a science which is growing rapidly, or, to speak less arrogantly and more correctly, our knowledge of the ways of protoplasm, the Chemist, has greatly increased during the last few years. We can but watch protoplasm at work. Our experiments, so called, are but windows which we open in the walls of his laboratory. We cannot take the work out of his hands. The methods of mineral chemistry are useless in this search for knowledge. And, naturally, the longer we watch, the more details do we discover in what seemed at first a generalized procedure. We recognize that several manipulations are required in the carrying out of a reaction which hitherto we believed to take place in a single stage. This is not the place in which to give an account of a subject regarded as belonging, owing to its applications, to the province of pathology. But Nature is one, however many be the companies into which we divide the explorers of her secrets. We have attempted the merest outline of the observations made up to the present, and have submitted the results for the sake of the light which they throw upon the way in which ferments are prepared as they are wanted to meet the needs of normal every-day digestion and metabolism, rather than for the purpose of showing the methods by which protoplasm combats disease.
Amongst the chemical phenomena of life is respiration. Respiration in this very general sense means oxidation. The force which is exhibited in living is obtained from the union of organic materials with oxygen under the direction of protoplasm. This is true of plants as well as of animals. It is true even of the subdivision of bacteria, termed anaerobic, because they cannot live in air. They secrete ferments which enable them to decompose compounds which contain oxygen, in order that they may use the oxygen for respiration. It might have been supposed that green plants which are receiving radiant energy from the sun would convert this energy into the forces which enable protoplasm to display the phenomena of life. But this is not so. The energy which green plants obtain from the sun is used in constructive metabolism, and not in maintaining life. Life-force, if we may use the expression, is derived from the oxidation of the substances which the sun’s rays enable the plant to make. A plant, equally with an animal, respires. The distinction between the constructive metabolism of a plant and its respiration may be brought out in a striking way by administering to it sufficient anæsthetic to stop the former without stopping the latter. It may be paralyzed without being killed. If a water-weed—potamogeton is the most convenient—enclosed in a bell-glass filled with water and inverted over a dish of water, is placed in sunshine, bubbles of gas rise from the plant. They accumulate at the top of the bell-glass. If the gas be removed and analysed, it is found to be oxygen with a small admixture of carbonic acid. If a second bell-glass containing water-weed be exposed under the same conditions in all respects, save that a small quantity of chloroform is added to the water, the gas that collects at the top of the bell-jar will be much less in amount. It will be found to be carbonic acid without admixture of oxygen. The power which chlorophyll possesses of decomposing carbonic acid with fixation of carbon and liberation of oxygen is suspended by the anæsthetic; whereas respiration is not interfered with.
Lastly, we must attribute to protoplasm a capacity of growing. The activity of protoplasm depends upon constant molecular interchange. It incorporates molecules of food. It excorporates molecules of waste. If food is abundant and “vitality” exuberant, it takes in more than it gives out. It grows.
If we attempt to formulate a definition of protoplasm, we find that our ideas are far from clear, owing to want of knowledge. The questions, What is protoplasm? What is life? are equally unanswerable. Their definition is reciprocal. Protoplasm is the substance, the material, which exhibits life. Life is the complex of phenomena exhibited by protoplasm. All parts of the body are alive, in their degree. The nucleus of a cell lives, as well as its cell-body. Its capsule may be less alive—that is to say, less vibrant—than the soft cell-substance which it encloses; but it lives. So-called intercellular substance, or matrix, is alive. In growing cartilage the matrix does not behave as a dead substance. It does not crack and gape under the pressure of the dividing and multiplying cell-bodies which it contains. If the windows of a house were endowed with the power of spontaneously enlarging, the walls would be crushed. They would bulge, break, tumble. The matrix of cartilage offers as little resistance to the enlargement of the cells which it encloses as the plasma of blood to the multiplication of blood-corpuscles. It grows with the cell-bodies, and must be considered as divisible into areas, each of which is the periphery of a cell. Muscle is alive. So, too, are bone, teeth, hair, nails. But as we proceed outwards we find the quality of aliveness growing less and less apparent, until at last we acknowledge that it is unrecognizable. Vibrations diminish in amplitude and in rapidity, until the material of which the body is made appears to be at rest.
Biologists apply the term “protoplasm” to the most living substance of which plants and animals are composed. It may be that there is an entity, protoplasm. It may be that in certain situations this exists in an unmixed state. It may be that the degree of aliveness of a tissue or constituent part of a tissue varies as the quantity of protoplasm which it contains. The tendency of protoplasm to dispose itself in a reticulum in the meshes of which other substances accumulate favours such a view. The cells of the deeper layers of the skin are rich in it. The superficial layers are composed chiefly of keratin. It is possible that the network opens out, and its strands grow thinner and thinner, as keratin accumulates. But it cannot be demonstrated that this is the case. There is no completely satisfactory reason for concluding that the life of a cell of the skin resides in its protoplasmic network, while its keratin is inert.
Many attempts have been made to prove that living cells contain something which dead cells do not contain; but no evidence which will bear sifting has, as yet, been adduced in support of this thesis.