,28 



A MANUAL OF PHYSIOLOGY 



ferments, according to the conditions (Kastle and Loevenhart). 

 The perfectly aseptic blood does not split ordinary neutral fats, 

 although it contains a ferment which splits up monobutyrin 

 (glycerin butyrate) into glycerin and butyric acid. 



Summary. At this point let us sum up what we have learnt 

 as to the relation between the proximate principles of the tissues 

 and the proximate principles of the food. Inside the body we 

 recognise representatives of the three groups of organic food-sub- 

 stances in a typical diet proteins, carbo-hydrates, and fats. But 

 we should greatly err if we were to imagine that the three streams 

 of food-materials have flowed from the intestines into the tissues 

 each in its separate channel, neither giving to nor taking from 

 the others. The fats of the body may, indeed, in part be composed of 

 molecules which were present as fat in the food ; but they may also 

 be formed from carbo-hydrates, and probably from proteins. The 

 carbo-hydrates of the body the glycogen of the liver and muscles, the 

 sugar of the blood may undoubtedly be derived from carbo-hydrates 

 in the food, but they may also be derived from proteins, although 

 probably not from fats (except from their glycerin constituent). 

 The proteins of the body arise solely from the proteins of the food ; 

 neither fats nor carbo-hydrates can form proteins, although both can 

 economize them and shield them from an over-hasty metabolism. 



4. The Income and Expenditure of the Body (i) Income and 

 Expenditure of Nitrogen. 



Preliminary Data. The office of the food is to maintain the con- 

 stituents of the body upon the whole in their normal proportions. 

 A knowledge of the chemical composition of the body is, therefore, 

 an important datum in the consideration of the statistics of its 

 metabolism. The body of a man analyzed by Volkmann had the 

 following composition : 



Inorganic substances 

 Organic substances 



/Water 



\Mineral matter 

 /Carbon 18*4 

 [Hydrogen 2*7 

 "j Nitrogen 2' 6 

 (Oxygen 6 - o 



per 



cent. 



65 '9 per cent. 

 4'4 



297 



The muscles, the adipose tissue, and the skeleton form nearly 

 four-fifths of the total body-weight in the adult. The following 

 table shows the percentage amount of each of these tissues in a man, 

 a woman, and a child (Bischoff) : 



