Biochemistry

“ Bacteria make use of proteins chiefly as a source of nitrogen, but also as a source of carbon and other elements. Proteins contain nitrogen, carbon, hydrogen, oxygen, sulphur and frequently phosphorus. Some of the metals—potassium, sodium, calcium, magnesium, iron and manganese and the non-metal chlorine—are nearly always associated with them more or less intimately. Since these bodies are the most complex of natural chemical substances it follows that the breaking up of the molecule to secure a part of the nitrogen gives rise to a great variety of products. ”

“ So much for the outside sac of the cell—now for the inside. The cell-jelly, or proto-plasm, is made of water, fat, mineral matters, and protein. The water we already know. The fat is made of carbon, hydrogen, and oxygen. The minerals belong to the simple elements.
The protein we know but little about. We are sure that it contains carbon, hydrogen, oxygen, and nitrogen, with a little sulphur or phosphorus, or both, and we know that it is found in all living matter. There is no life without it, so it has been called the "basis of life." ”

“ Where the analytical powers of the microscope in anatomy can go no farther, chemical analysis of the composition of the cell steps in. By its means the discovery is made that there is no elementary difference between organic and inorganic nature, for only such chemical elements as are known to exist in the inorganic world are found in the organic. On the other hand, however, the living cell-substance possesses chemical compounds which find analogues nowhere in inorganic nature. The characteristic organic substances which are present in every cell are proteids and proteid-compounds. ”

“ With the time at my disposal, it would be impossible to discuss all the chemico-vital problems which the physiologists of the present day are attempting to solve, but there is one subject at which many of them are laboring which seems to me to be of supreme importance—I mean the chemical constitution of proteid or albuminous substances. Proteids are produced only in the living laboratory of plants and animals; proteid metabolism is the main chemical attribute of a living thing; proteid matter is the all-important material present in protoplasm. ”

“ In the present state of our knowledge concerning the functioning of the proteins, no significance in the physiology of plant life, or metabolism, is to be attached to the particular type of protein material which it contains, at least so far as the simple proteins of the cytoplasm are concerned. ”

“ Of these, carbon and oxygen unite, in certain proportions and under certain conditions, to give rise to carbonic acid; hydrogen and oxygen produce water; nitrogen and hydrogen give rise to ammonia. These new compounds, like the elementary bodies of which they are composed, are lifeless. But when they are brought together under certain conditions they give rise to the still more complex body, protoplasm, and this protoplasm exhibits the phenomena of life.’
Until we have further knowledge of the changes which constitute these phenomena, physiology must remain descriptive rather than explanatory. ”

“ The chemical materialist conceives certain compounds, never well-known ones mark you, enzymes for example, to be thus supremely endowed. The biological materialist on the other hand, ascribes this exalted role to imaginary, invisible living bodies hidden deep within the germ and other cells. Biology of the last three decades has bestowed mighty powers upon such bodies under the designation "determinants." Only those familiar with the technical literature of the science during this time can have any notion of the influence these bodies have had. ”

“ To enable us to say that we know anything about the experimental origination of organisation and life, the investigator ought to be able to take inorganic matters, such as carbonic acid, ammonia, water, and salines, in any sort of inorganic combination, and be able to build them up into protein matter, and then that protein matter ought to begin to live in an organic form. ”

“ The mysteries of organic chemistry are great, and the differences between its processes or reactions as they are carried out in the organism and in the laboratory are many421. The actions, catalytic and other, which go on in the living cell are of extraordinary complexity. But the contention that they are different in kind from what we term ordinary chemical operations, or that in the production of single asymmetric compounds there is actually to be witnessed, as Pasteur maintained, a “prerogative of life,” would seem to be no longer safely tenable. ”

“ The higher we climb in the scale of organization, particularly in the animal kingdom, the more do we meet with cells which are entrusted with special functions. For instance, we find cells which receive matter from the exterior. Others transform particular compounds into products of a special nature. Others, again, have the function of carrying the final products of metabolism to definite points for excretion.
A unicellular organism stands constantly in relation with numerous substances of the outer world, which differ from place to place and from time to time.. ”

“ Enzymes are found in all parts of the animal organism and those which are active in the digestion of food, the metabolism of digested material, the coagulation of blood, etc., have been extensively studied. A discussion of these animal enzymes would be out of place in such a text as this, however, and the following list includes only enzymes which are known to occur in plant tissues. ”

“ We see that the substances classed as ferments, which, during their own molecular changes, set up molecular changes in the accompanying carbo-hydrates, are all nitrogenous. We see that among classes of organisms, and among the parts of each organism, there is a relation between the amount of nitrogenous matter present and the amount of independent activity. And we see that even in organisms and parts of organisms where the activity is least, such changes as do take place are initiated by a substance containing nitrogen. ”

“ On the other hand, the morphologist will urge that green plants derive their peculiar powers of metabolism from the possession of very definite cell-organs, namely chromatophores containing chlorophyll; and will argue that living things without such organs must have preceded in evolution those possessing them. The whole dispute is based on the assumption that plant and animal represent the two fundamental modes of metabolism; whereas the study of the Bacteria shows the possibility of many other modes of life. ”

“ The differentiation of nucleus and protoplasm in the living substance of the cell alone gives rise to an extraordinary complication in the metabolic process, for these two parts of the cell stand in the most complicated correlation with Cell-Processes the Secret of Life. one another as well as with the environing medium—a fact of which the experiments made by vivisection in various free-living cell-forms have furnished abundant evidence. The farther such knowledge advances, the more rounded, clear and free from hypotheses will become our conception of the cell's metabolism. ”

“ We conceive that, in the primordial world, as now in the laboratory, higher types of organic substance were formed at the expense of lower types, and that gradually, after repeated reactions and under favorable conditions, they resulted in organizable protoplasm, a substance which is very susceptible of modification. Protein, as we know, may exist in upward of one thousand isomeric forms, and, by combination with itself and with other substances, it yields products still more complex, and in countless numbers. ”

“ This difference consists in the vegetable feeding upon inorganic food, and the animal on food which has received the stamp of organisation. Creatures possessing life, whether vegetable or animal, are called organisms. It is found that these organisms are made up of certain atoms united in larger multiples than in inorganic substances, which are either simple or compounded of but few atoms; thus water is composed (every atom of it) of one atom oxygen, united to two of hydrogen. Common salt (every atom of it) is composed of one atom of the metal sodium with one atom of chlorine. ”

“ So far as is known, the peculiar substances called enzymes are produced only by the living cells of animals and plants, although there are certain inorganic substances that so closely reproduce the essential qualities of enzyme action that they might almost be termed 'inorganic enzymes.' The enzymes obtained from the animal or plant cell have never been isolated in a pure condition, and hence no definite knowledge of their chemical composition and constitution has yet been secured. ”

“ But all our experience, hitherto, has proved, that even those cells which are constructed on a simple plan morphologically do, when studied from a purely chemical point of view, show exceedingly complicated relations. Indeed, the study of the processes of metabolism in unicellular forms of life is a study all the more difficult, in comparison with that of more complicated organisms, in that, in the former, it is so difficult to separate the actually absorbed materials from the metabolic by-products, and these again from the secretory or excretory products. ”

“ An exhaustive study of the sources of nitrogen necessary for each separate organism, paying due attention to other nutritious materials and conditions, will no doubt lead to exact methods for the culture of separate cells in the laboratory. Following this line of inquiry we could surround certain microorganisms with peptones whose composition we are familiar with, and so acquire a deeper insight into the processes of their metabolism. ”

“ Everything points to the fact that the cell has agents at its disposal which render it capable of splitting up, into their simplest units, all the complicated substances which are brought to it, or which it itself builds up. In favour of such a view, we may more particularly cite, besides the direct proof of the existence of ferments, the observation that in the metabolism of the cell all the units, out of which the complicated nutritive substances and the components of the cells are built up, are found to occur. ”

“ We come next to the agency of chief importance among those that work changes in organic matter; namely, chemical affinity. How readily vegetal and animal substances are modified by other substances put in contact with them, we see daily illustrated. Besides the many compounds which cause the death of an organism into which they are put, we have the much greater number of compounds which work those milder effects termed medicinal—effects implying, like the others, molecular re-arrangements. ”

“ Protoplasm, the living material, contains only a few elements, all of which are extremely common and none of which is peculiar to it. These elements, however, form compounds characteristic of living substance and for the most part peculiar to it. Proteid, which consists of carbon, hydrogen, nitrogen, oxygen and sulphur, is present in all protoplasm, is the most complex of all organic bodies, and, so far, is known only from organic bodies. ”

“ The chemists have proved that all elementary organic substances consist of carbon, hydrogen, oxygen, and nitrogen, susceptible of endless modifications of their respective forces, under which an organic molecule or ovum is produced, and after that, under certain circumstances, an animal such as man. ”

“ The staggering difficulties in imagining such a possibility are not merely on the chemical side—e. g., the produc­tion of proteins from CO2, and N—but also on the physical side if the necessity of a definite cell structure is considered. We shall see in the sixth chapter that without a structure in the egg to begin with, no forma­tion of a complicated organism is imaginable; and while a bacterium may have a simple structure, such a structure as it possesses is as necessary for its existence as are its enzymes. ”

“ Certain substances, called enzymes, formed by glands cause the digestion of food. The enzymes secreted by the cells of the glands and poured out into the food tube act upon insoluble foods so as to change them to a soluble form. They are the product of the activity of the cell, although they are not themselves alive. We do not know much about enzymes themselves, but we can observe what they do. Some enzymes render soluble different foods, others work in the blood, still others probably act within any cell of the body as an aid to oxidation, when work is done. ”

“ The condensation of amino-acids into proteins, or the reverse decomposition, is very readily accomplished in all living protoplasm, under the influence of special protein-attacking enzymes, which are almost universally present in the cytoplasm. ”

“ And, notwithstanding the immense progress that modern chemistry has made within the last ten years, its art is still limited at this point: no prospect yet exists that it will be able, artificially, to produce the most important of all the substances that go to build up the bodies of animals and plants, and to form their living cell-tissues—protoplasm, or the envelope of the plant-cells, the matter of the muscles and nerves. ”

“ Nothing is known with certainty concerning the chemical nature of enzymes. Being colloidal in nature, they adsorb carbohydrates, proteins, fats, etc., so that active enzyme preparations often respond to the characteristic tests for these groups of substances ”

“ The mention of physical chemistry brings me to what I may term the second head of my discourse, the second striking characteristic of modern chemical physiology: this is the increasing importance which physiologists recognize in a study of inorganic chemistry. The materials of which our bodies are composed are mainly organic compounds, among which the proteids stand out as preeminently important; but every one knows there are many substances of the mineral or inorganic kingdom present in addition. ”