A Text-book of medical practice for practitioners and students / edited by William Bain.
- Date:
- 1904
Licence: In copyright
Credit: A Text-book of medical practice for practitioners and students / edited by William Bain. Source: Wellcome Collection.
Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.
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![CHEMICAL CONSTITUTION OF THE ANIMAL BODY. Analysis of the body shows that it is constituted from the following elements : Carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, chlorine, iodine, sodium, potassiuu;, iron, calcium, magnesium and occasionally fluorine, silicon and manganese. The com- pounds most abundantly present, and therefore the most important, are all carbon com- pounds of some complexity and of these the most common—namely the proteids—also contain nitrogen. The animal organism is dependent for its energy upon a supply of chemical substances (foods) in themselves complex and capable of giving out their energy on combustion. The essential chemical process taking place within the body is that of oxidation, for the final products eliminated as the result of the complete series of changes are such bodies as water, carbonic acid, urea, etc., i.e., bodies of very simjile nature and such as are formed by the complete combustion of those substances outside the body. But although oxidation and complete disintegration are thus the processes by means of which the final result is obtained, the animal organism, like the vegetable, possesses con- siderable synthetic powers, as is, for instance, seen in the formation of complex proteids from relatively simple ones taken in the food, or again in the power of building up fats from carbohydrates. The foods of an animal are derived for the most part from other living organisms, vegetable or animal. Hence the chemistry of the body is also to a large extent the chemistry of the food stuffs. In this relation the substances we have to examine can be grouped into four classes, viz., proteids, fats, carbohydrates, salts and water. Peoteids. The proteids are by far the most complex bodies, and are only to be obtained from living organisms. They are, indeed, characteristic of protoplasm. They possess no decided acid or basic properties. They all contain C, H, N, O, S, and at times P. They are tasteless, amorphous, indifiusible, and form viscid solutions. An idea of their coni- plexity can be gained from a study of the amount of sulphur they contain and the way it is combined within the molecule. Part of this sulphur is fully oxidised, part unoxidised, since it can be split off as suljihide by Iwiling the proteid with strong alkali. Hence there must be at least two sulphur atoms in the ]jroteid molecule, and wlien, from this as a basis, we calculate tlie number of the other atoms necessarily present we find that they have to be estimated by hundreds. In attempting to gain an insight into the struc- ture of the molecule our best procedure is to break it down step by step and deternune the various bodies that are thereby produced. The most effective way is to hydrolyse it, e.g., by ferments, by superheated steam or by acids or alkalis. As a prehmmary step, it is best to find out what bodies are produced by complete hydrolysis, and we may then examine the intermediate stages. On decomposition with a mineral acid, a proteid gives a very complex mixture of nitrogenous carbon compounds consisting chiefly of members of the fatty acid series, and to a less degree of compounds containing an aromatic nucleus They are, for the most part, amido-acids, but nitrogenous bases are also ]H-oduced including ammonia. Tlius, we find alanine, leucine, aspartic acid, glutammic acid and sometimes glycine, all amido-acids of the fatty series ; phenyl-alanine and tyrosine which contain radicles of both scries ; the hexone l)ascs, lysine, arginine and js'^'^}?/ monia; and a-i)yrollidine-carboxylic acid. Alanine is amido-propionic acid CH,, t H(IN H,) COOK. Leucine is amido-caproic acid, O4H,,. CHCNH^) . COOH. Aspartic acid ,s anndo- succinic acid, CH„(C()()H) . CH(NH2) . COOH. Glutaminic acid is amido-pyn.tarta^^^^ acid, CH2 (COOH). CH,. CH(NH2). COOH. Glycine is amido-acetic acid, CH2(NH2). COOH. Phenyl-alanine is phenyl-amido-propionic acid, and tyrosine is para-(.xy|ilienyl- amido-propioniJ acid, i.e., c]^,. CH,. CH(NH.,) COOH. and CeH,(OH). CH,. CPf(NH,). COOH. respectively. The hexone bases are so called because they contain six carbon atoms. Lysine is diamido-caproic acid, Cfilli .N^Oa ; argjnme, C^H^NM, is tiie urome of diamido-valerianic acid ; and histidine has the formula C^H^N/),, but its structure is still unknown. Pyrollidine-carboxylic acid is a derivative of the pyrrol (O^MiiM) series](https://iiif.wellcomecollection.org/image/b21510167_0050.jp2/full/800%2C/0/default.jpg)
