8 7 : 
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 1 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 : — 
Incomings. 
Outgoings. 
Foodstuffs. 
N. 
c. 
Excreta. 
X. 
C. 
Proteids . 137grms. 
Fat . . 117 „ 
Carbo-hydrates 352 ,, 
19-5 
1 
\ 315-5 
) 
Urine 
Faces 
Respiration 
17-4 
2-1 
12-6 
14-5 
248-6 
19-5 
315-5 19-5 275-7 
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 
aldehvde compounds, whereas it is well known that dead proteid yields bodies 
of an amide nature. - 
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. Yoit, Hermann's "Handbuch," Bd. vi. S. 513. The table in the simplified form 
here given is from Neumeister, "Lehrbuch," Jena, 1897, Anfl. 2, S. 344. 
- if. Halliburton, this Text-book, vol. i. p. 38. 
