86 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



organic alkaloids and indifferent crystalline bodies, some of which contain 

 sulphur, are other members of this group. As yet only three substances 

 of organic origin are known to contain phosphorus ; these are lecithin 

 (found in the blood, bile, and serous fluids), glycerin-phosphoric acid 

 (derived from the former, and found in the same localities), and nuclein 

 (found in pus-corpuscles, yelk of egg, and semen). In the living organism 

 these organic compounds are in a state of solution in a relatively large 

 amount of water, and either associated or chemically united with a small 

 percentage of inorganic matter, which modifies, in all probability, the 

 nature of the former, and is itself not without value in the vital processes. 

 All organic compounds are readily decomposable, either through the 

 action of various chemical reagents, elevation of temperature, or through 

 the processes of fermentation and putrefaction. As the result of all these 

 changes in organic matters simpler compounds are produced. The more 

 complex the molecule of organic matter, the more readily is it subjected to 

 decomposition. The character of these changes, as well as the nature of 

 some of the substances which result from change of various kinds in 

 organic matter, will be subsequently discussed. 



Of the inorganic constituents of cells by far the most abundant is 

 water, which forms the great bulk of organic bodies. Many vegetable 

 matters may contain as much as 90 per cent, of water, while the animal 

 tissues may contain 75 per cent, or more, though the percentage is by no 

 means constant, and may vary in single tissues according to different 

 physiological or pathological conditions. The inorganic constituents of 

 cells are taken up by the cells already preformed, and, as a rule, again 

 leave the cells in the form in which they entered it. The most prominent 

 exception to this rule is found in the case of carbon dioxide and sul- 

 phuric acid ; the former originating in the oxidation of the hydrogen 

 contained in the water of organic constituents, and the latter coming 

 from the oxidation of the sulphur contained in albuminoids. The inor- 

 o-anic constituents of animal and vegetable cells in no way differ from 

 similar bodies found in inorganic matter. When found as constituents 

 of cells the j' have invariably been derived from the atmosphere or the 

 earth, have been absorbed, often without undergoing any change, by 

 vegetable cells, and have passed from the latter into the interior of animal 

 tissues. Inorganic matter is found in all animal fluids and tissues, 

 although with great variation as to amount. Certain inorganic constitu- 

 ents — such, for example, as water and sodium chloride — are found 

 invariably in all animal tissues and fluids, while other of the inorganic 

 cell-constituents are limited to the cells of certain special tissues. 



The inorganic constituents of cells may exist either in the form of 

 gases, salts, free acids, or in certain forms of combination whose exact 

 arrangement has not yet been made out. 



