692 PHYSIOLOGY 



biological value of proteins. These differences in nitrogen value were 

 determined by Thomas in the following way. On a diet containing large 

 quantities of starch and sugar and only a trace of protein he found the 

 minimal loss of body protein. He then investigated how much of each 

 of the various proteins must be added to the diet in order to prevent any 

 loss of tissue protein. He arrived at the following biological values for 

 the proteins investigated : 



Ox meat 104 Cherry juice . . 79 



Cows' milk . . . .100 Yeast . .71 



Fish 95 Casein ... .70 



Rice 88 Nutrose 69 



Cauliflower .... 84 Spinach . . 64 



Crab meat 79 Peas .56 



Potatoes 79 Wheat flour . . 40 



Cornmeal . . 30 



The practical outcome of this experiment is that when there is scarcity 

 of protein, animal protein is more economical than vegetable protein, and 

 that if it is necessary to live on a purely vegetable diet this should be mixed, 

 so that all the amino-acids required in the body may be represented in the 

 diet. 



THE INORGANIC FOODSTUFFS 



If an animal be fed with the proper quantities of fats, proteins, and 

 carbohydrates, from which all the salts have been removed as completely 

 as possible, it rapidly shows a distaste for the food, becomes ill, and dies in 

 a shorter time than if it were receiving no food at all. Part of the symptoms 

 which occur in these cases are due to the production of acid substances, e. g. 

 sulphuric acid, in the course of metabolism of the proteins. It is possible 

 to obviate this acid intoxication by administering sodium carbonate with 

 the food. This admixture however suffices to prolong the life of the animal 

 only for a short time. It is evident therefore that the inorganic constitu- 

 ents of the food, although yielding no energy to the body, are as essential for 

 the maintenance of life as the energy-yielding foodstuffs, namely, proteins, 

 carbohydrates, and fats. In the course of 'this work we shall have occasion 

 to study the intimate dependence of the functions of various tissues, such as 

 skeletal and heart muscle, on the presence of salts in normal proportions in 

 the fluids with which they are bathed. Animals in a state of salt hunger show 

 by the disorders of digestion which occur that the presence of salts is equally 

 requisite for the due performance of the processes of secretion and absorption. 

 Towards the end of the experiment the animal vomits its food, which shows 

 no signs of digestion even when it has lain some hours in the stomach. 

 Forster has shown that in salt-hunger the body is continually giving off 

 inorganic constituents in the urine. The amount of these is smallest when 

 it is supplied richly with organic foodstuffs. It seems that the salts of the 

 body exist in a state of unstable combination with the tissue constituents, 

 especially the proteins. If the amount of food supplied is insufficient, the 

 animal lives on its own tissues, thus setting free salts which appear in the 



