144 SCIENCE PROGRESS. 



(" Fleischgewicht ") it contains. The non-nitrogenous con- 

 stituents of the body, such as glycogen and fat, are dead 

 material, and do not affect the metabolic requirements. 

 Only the proteids of the body are living. Hence a fat 

 animal has apparently a small nitrogenous metabolism, in 

 comparison to its weight, so much of this being due to dead 

 ballast. 



This view of the predominant importance of proteids for 

 the performance of muscular work is consonant with the 

 ideas on the subject which we in England have acquired 

 from our experience in training men and animals to be the 

 best muscular machines possible. The essence of training 

 consists in increasing the quantity of proteids in the food, 

 diminishing the carbohydrates and fats, and exercising all 

 the muscles as much as possible. But in spite of Prliiger's 

 arguments, we have no definite facts to exclude the possi- 

 bility of sugar being the immediate source of muscular 

 energy. We know for a certainty that sugar and glycogen 

 may be formed from proteid, and this formation may go on 

 in Prliiger's dog which is fed with a purely proteid diet. 

 An increase in the amount of work done would necessitate 

 the production of a greater quantity of sugar, and since this 

 can only come from proteid, there must be a greater disin- 

 tegration of proteid and an increased excretion of urea, so 

 that this increased excretion would be merely a secondary 

 result of the doing of work. It is still quite possible that, 

 as Bunge concludes, muscular work may be performed at 

 the expense of any of the three classes of food-stuffs. The 

 strongest argument in favour of Liebig and Prliiger's views 

 is still, not their carefully carried out experiments, but our 

 common experience that a man would run a mile better on 

 beefsteaks than on pounds of grape sugar. 



ON THE FORMATION OF FAT IN THE BODY. 



It is generally considered that fat may be formed from 

 all three classes of food-stuffs, and Voit looked upon proteid 

 as the chief, if not the only source, of fat, the fats and carbo- 

 hydrates of the food only increasing the fat of the body by 

 their sparing influence on the proteids of the food. The 



