CHEMISTRY, PHYSIOLOGICAL. One of the biological sciences, having for its object the study and investigation of the manifold chem ical processes taking place in living organisms, both animal and vegetable. Physical, or me chanical. physiology deals with those functions of living organisms explainable by physical laws and studied by physical methods. Chemical physiology. or physiological ehemistry, deals with those functions explainable by chemical laws and 'studied by chemical methods. In the study of chemistry, therefore, the facts to be col listed and the methods pursued are al most wholly chemical, while the application is purely physiological.
In the early days of physiological chemistry, energy was devoted mainly to the simple study of chemical composition. The various tissues hnd organs. especially of the higher animals, analyzed. their chemical composition cx :unified, and the chemical nature of the various proximate principles occurring in these tissues ascertained. It was found that twelve chemical elements enter into the composition of all living organisms—viz. carbon, nitrogen, hydrogen. oxy gen. sulphur. phosphorus, chlorine, sodium. po tassium. calcium. magnesium. and iron—while more recently iodine has been found widely dis tributed in organic combination. The first six of the above elements cuter mainly into the make-up of the organic of the living body. while the last six occur chiefly as inorganic or mineral compounds. Sulphur and phosphorus. however. are especially characterized by the fact that they are widely distributed in organic combination—that is, as an integral part of complex organic compounds. as proteids, nucleo proteids, and various crystalline substances— while at the same time in oxidized form as sul phates and phosphates of the alkalies and alkali earths, they are ever present as part of the inorganic salts. or mineral matter. so abundant in animal and vegetable tissues. Iron likewise occurs both in organic combination, as in fer ruginous nucleo-proteids and in the pigment of the red Idood-corpuscles, and in the form of simple iron salts. The ideas of physiologists, were revolutionized, and physiological chemistry took on new dignity. when it was seen that the various chemical substances—both simple and complex—formed in the tissues of living organ isms could be constructed in the laboratory by comparatively simple methods. (See ('ue.mts TRY. ) As a result, there rapidly developed great activity in the study of the chemical nature and chemical relationship of the organic compounds occurring in the body; methods were devised for producing them artificially; their genetic rela tionships were traced out; and much light was thrown upon the conditions attending their for mation in the hody. To-day the study of the chemical constitution of the various end-prod ucts of catabolism formed in and excreted from the body has given most useful infforIllat ion re garding a host of processes occurring in the organism. and has enabled the physiologist
to trace out many of the individual steps in the breaking down of complex organic material. In other words, chemical methods and simple chem ical principles are quite sufficient to explain the nature of the many processes going on in organisms by which the life and activity of the organism are maintained.
The various chemical processes charaeteristie of living organisms may he divided into main groups—viz. synthetic and analytic: i.e. building up and breaking down. Synthetical processes are most prominent in the vegetable kingdom. The plant-cell alone has the power of building up complex organic compounds out of simple elementary substances. The most strik ing illustration of this constructive power is seen in the formation of ifroteid or albuminous material. This important constituent of every living cell, in part the chemical hasis of proto plasm, originates solely through the synthetical power of the plant-cell. The earbonic acid of the atmosphere furnishes the carbon, hydrogen is drawn from the moisture. nitrogen from am Monia or nitrates in the air and water. oxygen from the air, sulphur and phosphorus from the sulphates and phosphates of the soil. From these elements proteid, the most complex organic substance known in nature. is constructed. As indicative of its chemical con posit ion, we ascribe to it formulie according to its exact nature, for there are many different pro teids in both the animal and vegetable king Morns. is represented by the for mula vegetable globulin, by the forum C..„,„I 1 „,,N,„o„S, The proteid of the animal kingdom is simply an alteration product of the vegetable synthetic product. The animal cell can simply transform and modify, but it cannot construct proteid; that is the province of the vegetable cell only. Synthetical processes, however, do occur in the animal kingdom. hint they are limited in extent. A good illustration is afforded by the formation of hippuric acid in the kidneys. Glyeocoll and benzoyl containing on pa ssing through the kidney, are, under the influence of the epithelial cells of the kidney and the ever present blood, made to combine, and hippurie acid results. This reaction may be formulated as follows: CH, ( N1 l„) COOH = Glyeocoll Benzoic acid + Hippuric 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.