660 THE NORMAL DIET. [Book ii. 



may continue in nitrogenous equilibrium and in good health 

 with a daily ration of much less than 100 grm. proteid, with 

 as little as 40 grm. for example. To this we shall have to 

 refer in speaking of a vegetable diet. Against the statistical 

 diet on the other hand we may urge that instinct is not an 

 unerring guide, and that the choice of a diet is determined by 

 many other circumstances than the physiological value of the 

 food. 



S 441. Taking however some such diet as the above to be 



O " -a • 



the approximately true normal diet, we may call attention to 

 the fact that the normal diet is made up of each of the three 

 great food-stuffs, carbohydrates being in excess. We may here 

 remark incidently that the diets of both the carnivora and 

 herbivora agree with that of omnivora in containing all three 

 food-stuffs : they differ from each other as to the relative pro- 

 portions only. As we have seen, the body may be maintained 

 in equilibrium on proteid food alone ; but an exclusively pro- 

 teid diet is not only bought dearly in the market, but also paid 

 for dearly within the economy ; we are of course now speaking 

 of man. To obtain the necessary carbon out of the carbon 

 moiety of proteid unnecessary labour is thrown on the economy, 

 and the system tends to become blocked with the amides and 

 other nitrogenous waste arising out of the nitrogen moiety 

 simply thrown off to secure the carbon. 



Fats and carbohydrates are much more akin to each other 

 than is either to proteid; and if on the one hand, as (§ 435) 

 seems possible or even probable, the fat of the food and of the 

 body is converted into sugar either on its way to become built 

 up into the tissue or in the course of the changes taking place 

 outside the real living framework of the tissue by which it is 

 reduced to carbonic acid, and that on the other hand carbohy- 

 drates can furnish the fat whose presence in the body is neces- 

 sary, we might expect that carbohydrate alone without fat 

 might, with proteid, form a normal diet. But on this point 

 experience is probably to be trusted ; and we may infer that 

 in every normal diet some fat at least must be added to the 

 starches and the sugars. 



The advantage of this mixture is probably felt while the 

 food is as yet within the alimentary canal. What we have 

 learnt concerning digestion leads us to regard it as a compli- 

 cated process, and we cannot readily imagine that the proteo- 

 lytic, amylolytic and adipolytic changes run their several 

 courses, especially in the small and large intestine, apart from 

 and irrespective of each other. We are rather led to suppose 

 that the accompaniment of one set of changes, in some indirect 

 manner, favours the others ; and it is for that reason probably 

 that we take our food-stuffs not separately but mixed in the 

 same meal, often on the same plate and even in the same mouth- 



