CHEMICAL COMPOSITION OF HUMAN" BODY. 17 



Although, however, a large number of so-called organic 

 compounds have long ceased to be peculiar in being formed 

 only by living tissues, it will be well to notice some of the 

 chief characters of the more common kinds of organic 

 matter, inasmuch as they form a large part of all living 

 tissues, and many of them have, up to the present time, 

 been formed by the agency of life only. 



Among the peculiarities in the chemical characters of animal 

 substances the two following may be specially noticed : 



1. They are composed of a larger number of elements 

 than are present in the more common kinds of inorganic 

 matter. Thus the most abundant substances, as albumen, 

 fibrin, and gelatin, in the more highly organized tissues 

 of animals are composed of five elements carbon, hydro- 

 gen, oxygen, nitrogen, and sulphur. 



2. Not only are a large number of elements usually 

 combined in an organic compound, but a large number of 

 equivalents or atoms of each of the elements are united to 

 form an equivalent or atom of the compound. In the case 

 of carbonate of ammonia, as an example among inorganic 

 substances, one equivalent of carbonic acid is united with 

 one of ammonia ; the equivalent or atom of carbonic acid 

 consists of one of carbon with two of oxygen ; and that of 

 ammonia of one of nitrogen with three of hydrogen. But 

 in an equivalent or atom of fibrin, or of albumen, there 

 are of the same elements, respectively, 48, 15, 12, and 39 

 equivalents, according to Dumas, and nearly ten times as 

 many, according to Mulder. And, together with this union 

 of large numbers of equivalents in the organic compound, 

 it is further observable, that the several numbers stand in 

 no simple arithmetical relation one with another, as the 

 numbers of equivalents combining in an inorganic com- 

 pound do. 



With these peculiarities in the chemical composition of 

 organic bodies we may connect two other consequent facts ; 

 first, the large number of different compounds that are 



