GENERAL METABOLISM. 



661 



study of such problems for the complete understanding of the principles of 

 practical nutrition. 



It is very significant that even the adult organism requires nutriment 

 not only as fuel, but also for the constant construction and renewal of the 

 cells. It must never be forgotten that the organism is adjusted for a 

 mixed diet, and that certain kinds of stimulation are necessary for the 

 production of the digestive juices. It is not at all practical to consider 

 replacing our food with chemical products. Our knowledge regarding 

 the necessary nourishment for the organism is far too limited for us to 

 attack such problems. The attempt has been made quite recently to 

 provide albumin in as pure a form as possible for the use of the sick. Our 

 understanding of metabolism is not such that we can approve of such 

 experiments unreservedly. In paying a good deal of attention to a par- 

 ticular nutriment we are pretty sure to neglect something else. We have 

 seen from the Law of Isodynamics that the carbohydrates and fats replace 

 one another in accordance with their calorific values, and that protein may 

 be replaced by these two foodstuffs to a certain extent. There is always 

 danger, in making use of chemically -pure foods, that too little attention 

 will be paid to the amount of inorganic salts which are required. The 

 knowledge of the calorific requirements for the performance of a definite 

 amount of work is very important for the establishment of a ration. The 

 calorific requirement forms a foundation. It must not, however, be re- 

 garded as the sole requirement. The composition of the ration is by no 

 means a matter of absolute indifference. 



In the following table the calorific values of a few foodstuffs are given: 1 

 one gram of substance yields the following number of heat units, expressed 

 in small calories : 



(A) PROTEINS. 



(B) FATS. 



1 Cf. Konig: loc. ciL p. 283 et seq. 



