II. PHYSIOLOGIC CHEMISTRY. 



PHYSIOLOGIC chemistry, as applied to the human body, may 

 be defined as the science which treats of the ingredients of the human 

 body and of the human food. These ingredients are spoken of by 

 some writers as " proximate principles," by others as the " chemical 

 basis/' and by still others as " physiologic ingredients." The latter 

 term is the one which will be adopted, as it is the most expressive. 



If the human body is analyzed into its ultimate chemical ele- 

 ments, it will be found that of the sixty-nine elements known to 

 chemists no less than fifteen are constantly present. These elements 

 are oxygen, carbon, hydrogen, nitrogen, calcium, sodium, potas- 

 sium, iron, phosphorus, sulphur, magnesium, chlorin, fluorin, sil- 

 icon, and iodin. Some authorities place lithium also in this list. 

 As fluorin and silicon occur in such small proportions, they may 

 be omitted from consideration altogether. 



To obtain most of these substances in their elementary form 

 such processes must be adopted as will utterly destroy the tissues. 

 In the body, in its living state, most of these substances do not 

 exist in their elementary condition ; and, however interesting it 

 may be to know all the facts about them, still a knowledge of the 

 properties of these elements does not help to an understanding of 

 their offices in the human body. What is really desired to be 

 known is, under what forms these elements exist in the body during 

 life, and not what can be obtained by the analytic chemist. 



Chemical elements and physiologic ingredients are not inter- 

 changeable terms. A physiologic ingredient may be defined as 

 a substance which exists in the body under its own form. To deter- 

 mine, then, whether a given substance is or is not a physiologic 

 ingredient of the human body, it must be ascertained whether it 

 does or does not exist there under its own form. For instance, 

 if it is asked if carbon is a physiologic ingredient, before the 

 question could be answered we should have to determine whether 

 carbon exists in the body under its own form that is, as carbon. 



Chemistry demonstrates that carbon, as an element, is found in 

 nature in but three forms, namely, as coal, as the diamond, and as 

 graphite or plumbago. In the human body none of these sub- 

 stances is found ; therefore carbon does not exist under its own 

 form, and consequently is not a physiologic ingredient, although 



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