8 7 2 



METABOLISM, 



in amount. These substances are mainly the fats, to a much less 

 extent the carbohydrates, whereas the substances which form the 

 actual tissues are composed of proteids and nucleo-proteids. 



The following is an instance of a balance table : of a man weighing 70 

 kilos., showing nitrogenous equilibrium only, some of the carbon of the ingesta 

 (mostly representing stored fat) not reappearing in the excreta : 



Whether the material which forms the bioplasm of the tissues has an 

 essentially different molecular constitution during life from that which is met 

 with in it after death, is not certainly known, but is extremely probable. This 

 is obviously a point which is difficult of determination, because we cannot 

 investigate the material composing bioplasm without previously killing it. 

 All we are able to do is to determine, as far as possible, the changes which the 

 tissues undergo, by investigating the products which they give off during life. 

 Our knowledge of these products has led some physiologists to the conclusion 

 that the substance of living material is composed of unstable cyanogen or 

 aldehyde compounds, whereas it is well known that dead proteid yields bodies 

 of an amide nature. 2 



Composition of foodstuffs. The most important general fact that 

 we need concern ourselves with in this place regarding the composition 

 of foodstuffs is that, with ordinary mixed diet, they are composed in 

 certain not very definite proportions of three chief kinds of organic 

 material, namely, proteids, carbohydrates, and fats ; in addition to 

 which, water and salts are a necessary part of the food. The most 

 general proportion of these three primary varieties of foodstuffs 

 to one another in ordinary diet is found to be about one part of 

 proteid material to from four to six parts of non-proteid, while the non- 

 proteid constituents stand to one another in about the proportion of one 

 part of fat to from five to ten parts of carbohydrate, this ratio having 

 been arrived at by investigating the composition of freely chosen diets 

 of persons in various occupations and stations of life. At the same time, 

 it must be pointed out that departures from these proportions are by no 

 means unfrequently met with, and especially is this the case with 

 certain races of mankind, e.g. some of the Asiatic races, where a very 

 much larger proportion of non-proteid material is ordinarily taken with 

 the diet than is the case with Europeans ; whereas, on the contrary, in 

 parts of South America and Australia, where meat is plentiful, the pro- 

 portion of proteid to non-proteid may be far larger than that above given. 



1 C. Voit, Hermann's "Handbuch," Bd. vi. S. 513. The table in the simplified form 

 here given is from Neumeister, "Lehrbuch," Jena, 1897, Aufl. 2, S. 344. 



2 Cf. Halliburton, this Text-book, vol. i. p. 38. 



