THE PROBLEM OF FOOD n 



split off and excreted, while the non-nitrogenous part 

 is oxidized like carbohydrate or fat. It is possible, 

 however, that this latter part may be more easily or 

 more economically oxidized than the more complex 

 carbohydrate or fat. The recent observations of 

 Anderson and Lusk show that protein has no special 

 value in this respect. The amount of energy value 

 required by a dog to do a particular piece of work 

 was the same, whether derived from its own store or 

 from a diet of carbohydrate or of protein, namely, 

 0.580 kilogram metre per kilogram of body weight 

 transported i metre. It was, perhaps, rather less in 

 the case of carbohydrate. But what is of interest 

 in the present connection is that when protein was 

 used the extra amount of energy due to its ''specific 

 dynamic action" was given off in addition to that 

 utilized as work; hence playing no part. In other 

 words, when the work was done at the expenditure 

 of protein, the body lost more energy than when the 

 same work was done at the expense of carbohydrate. 

 It is difficult to avoid the conclusion that there was 

 waste. 



On the whole, the "specific dynamic action" appears 

 to be merely an incidental occurrence in the mode of 

 utilization of protein, of doubtful, if any, benefit. But 

 there still remains something to be cleared up. 



Accessory Factors or " Vitamines". It is now well 

 known that the presence of some substances in addition 

 to the ordinary fat, carbohydrate, and protein is neces- 

 sary in order that a diet may be adequate for growth, 

 and also in order that the appearance of certain 

 diseases may be avoided. For this reason these par- 

 ticular diseases are called "deficiency diseases". 



Although Captain Cook found out that scurvy could 

 be prevented by taking fresh fruit and vegetables, the 

 chemical nature of these "accessory factors" is still 



