Page:The New International Encyclopædia 1st ed. v. 04.djvu/661

* CHEMISTRY. 5" doms. Egg-albumin is rcpicseuted by the for- mula C.^^H3::Xi;Oo„S.; vegetable globulin, by the lorniula Ca,..H,siXBoOs3S.. The jnoteid of the animal kingdom is simply an alteratioiv product of the vegetable synthetic product. The animal cell can simply transform and nuKlify, but it cannot construct proteid; that is the piovince of the vegetable cell only. Synthetical processes, however, do occur in the animal kingdom, but they are limited in extent. A good illustration is arforded by the formation of hippurie acid in the kidneys. Glycocoll and any benzoyl - containing coniijound, on passing through the kidney, arc. under the inlluence of the ei)itlielial cells of the kidney and the ever- present blood, made to combine, and hippurie acid results. This reaction may be formulated as follows: CHj(XH,)COOH + CHjCOOH = GlveocoU Benzoic acid CoH,CO.XH.CH,COOH + H.O Hippurie acid Water As is evident from the reaction given, this form of synthetical operation does not involve much chemical transformation : two moderately complex substances are simply combined with liberation of a molecule of water, a process not to be compared with the building up of a com- plex albuminous body from simple groups or radicles. In the animal body analytical processes are most conspicuous. Here complex organic mate- rial is transformed and ultimately broken down with liberation of the energv* stored up in the large molecules, and which came primarily from the sun. These analytical or destructive changes are of various kinds, such as hydrolysis, oxida- tion, reduction, etc. Examples of hydrolytic decomposition or change are perhaps best seen in connection with the digestive processes. Here the various cla.sses of foodstuffs, under the influence of the diges- tive juices, are gradually transformed into more or less soluble and diffusible products well fitted for absorption. Proteid, for example, is eon- verted into a row of soluble proteoses and pep- tones : a transformation brought about by cer- tain enzjTiies or ferments, such as pepsin and trypsin. The change, little imderstood. is termed catalytic, since it is assumed to occur through mere contact of the enzyme ; but what really hap- l)ens is the taking on by the proteid of one or more molecules of water (hydrolysis) with sub- sequent si)litting or cleavage of the molecule, and formation of a number of simpler products. Hence, the products are frequently termed hydro- lytic cleavage products. A like transformation occurs in the digestion of starch with saliva or (lancreatic juice, whereby soluble dextrins and sugars result, under the influence of the enzTnes contained in the above secretions. Further, cane- sugar, under the influence of the invert ferment secreted by the intestinal cells, is split into two molecules of a simpler sugar during digestion, as a result of simple hydration. Tlie reaction which takes place may be represented as follows: CuH..p„ + H.O = C,H,.0, + C,H,,0„ Cane-sugar Dextrose Dextrose Hydrolytic processes of the above type are very common methods by which chemical changes are effected in the animal body. Oxidative changes are especially conspicuous in animal tissues. Oxidation is the principal 9 CHEMISTRY. method by whidi the organic material of the tis- sues is broken down. Naturally, this oxidation is brought about in sonic measure by the o.xygcn coming to the tissues in the arterial blood, but there are present in many, if not in all, tissucA of the animal body, as well as in vegetable tis- sues, jjcculiar ferments such as the oxidases which are capable of inciting oxidation. Many of the oxidative processes going on in the ani- mal body seem to be connected with the life of the cell of the tissue or organ involved, but it is quite probable that in most, if not in all, such cases there are really oxidizing enzymes present, generated no doubt by the activity of the cell. The best example of reduction ill the animal body is found in the changes going on in the lower end of the small intestine and at the be- ginning of the large intestine, where various reducing gases are generated through the grortli and activity of anaerobiotic bacteria. The.se mi- croorganisms are ever present in the intestine, and, as products of their growth, hydrogen, car- buretted hydrogen, hydrogen suli)hide. and car- bonic acid are formed in varying amounts. These reducing gases are quite able to reduce other sub- stances brought in contact with them in the in- testine, and it is in this way that the pigments of the urine and of the fjeces are formed from the bilirubin of the bile. The ultimate object of the various chemical processes occurring in the animal body is the liberation of the energy necessary to keep up the vital processes. Upon this ability depends life and all forms of vital activity. The potential energy of the foodstuffs, the fuel of the animal body, is derived from the sun. As Bunge has stated it, "all the potential energy of vegetable substances is converted sunlight." The food- stuffs, whether animal or vegetable, are rendered capable of absorption by the several digestive processes. After passing into the blood or lymph, they are carried to the various organs and tis- sues of the body, where they are assimilated, and, by processes of anabolism. are built up. in part, into the tissues of the body, or in part di- rectly burned with liberation of their energy. This energy shows itself either in the form of heat or as work — i.e. muscular movements, or organized movements by which we perform work. The sum of the work performed by an animal, and of the heat which it gives out, is the exact equivalent of the potential energy contained in the food taken in, or in the material of the tissues burned tip. This energy' is liljerated as the result of oxidation, and the energj- is essen- tially the same in amount, whether the oxidation is carried on in the body or by combustion out- side of the body. In other words, the amount of energy liberated is the same whether the food- stuff or its euivalent is burned directly to car- bonic acid and water, or whether it is broken down gradually, step by step, until the final stage in the oxidation is reached. A man of average body weight, doing an average amount of work, must consume food material sufficient to yield 3000 kilogram-degree units of heat, or 3000 large calories, if he is to keep himself in equilibrium. The amount of heat required to keep the body continuously at .3S' C, no matter what the temp<-rature of the surrounding air, is by no means small, and. in aildition. it is to be remembered that all the involuntary muscular movements, such as the beating of the heart, the