CHEMICAL CONSTITUTION OP THE ANIMAL BODY. 143 



hence we shall treat chemical details in the chapters devoted to 

 special physiology, and here give only such an outline as wUl 

 bring before the view the chemical composition of the body in 

 its main outlines ; and even many of these will gather a signifi- 

 cance, as the study of physiology progresses, that they can not 

 possibly have at the present. 



Fewer than one third of the chemical elements enter into 

 the composition of the mammalian body ; in fact, the great 

 bulk of the organism is composed of carbon, hydrogen, nitro- 

 gen, and oxygen ; sodium, potassium, magnesium, calcium, 

 sulphur, phosphorus, chlorine, iron, fluorine, silicon, though 

 occurring in very small quantity, seem to be indispensable to- 

 the living body ; while certain others are evidently only pres- 

 ent as foreign bodies or impurities to be thrown out sooner 

 or later. It need scarcely be said that the elements do not 

 occur as such in the living body, but in combination form- 

 ing salts, which latter are usually united with albuminous 

 compounds. As previously mentioned, the various parts which 

 make up the entire body of an animal are composed of living 

 matter in very diflEerent degrees ; hence we find in such parts 

 as the bones abundance of salts, relative to the proportion of 

 proteid matter; a condition demanded by that rigidity without 

 which an internal skeleton would be useless, a defect well illus- 

 trated by that disease of the bones known as rickets, in which 

 the lime-salts are insufficient. It is manifest that there may be 

 a very great variety of classifications of the compounds found 

 in the animal body according as we regard it from a chemical, 

 physical, or physiological point of view, or combine many 

 aspects in one whole. The latter is, of course, the most correct 

 and profitable method, and as such is impossible at this stage 

 of the student's progress ; we shall simply present him with the 

 following outline, which will be found both simple and com- 

 prehensive.* 



CHEMICAL CONSTITUTION OF THE BODY. 



Such food as supplies energy directly must contain carbon 

 compounds. 



Living matter or protoplasm always contains nitrogenous 

 carbon compounds. 



* Taken from the author's Outlines of Lectures on Physiology, W. Drys- 

 dale & Co., Montreal. 



