422 SCIENCE PROGRESS 



energy is at its disposal in the form of protein and fat, its 

 normal metabolism is undermined ; fats are incompletely burned, 

 all stability of protein metabolism disappears and health fails. 

 Carbohydrate, like protein, serves other purposes than that of 

 mere fuel and a minimum of the former is as necessary as a 

 minimum of the latter. The isodynamic law of Rubner holds 

 within limits only : carbohydrates and fats are not, au fond, 

 physiologically equivalent. One does not know how far this 

 fact may prove to have practical importance. Practical dietaries 

 probably all contain the necessary minimum of carbohydrate ; 

 but it is well to point out that for individual species an optimum 

 amount may exist not identical with the minimum. About this 

 we know nothing. It may quite well prove worth while to 

 determine more exactly the effect upon nutrition of altering the 

 carbohydrate : fat ratio during prolonged periods. 



Apart from considerations relating to the better known 

 constituents of foods, we know from the work of the past year 

 or two that quite unsuspected factors are essential to the 

 normality of diet. An absence from the animal's diet of 

 substances to which it is accustomed in very small amount may 

 produce startling results. Feed a man on intact rice grains and 

 he does well. Supply him with decorticated polished rice alone 

 and he develops disease of the severest type. Restore a sub- 

 stance present in very minute amount in the cortex of the grain 

 and you restore nutritive power to the polished grain. Feed 

 a young animal on an artificial mixture of pure protein, fat, 

 carbohydrate and salts and it ceases to grow, even when the 

 amount consumed is quantitatively adequate. Add to the arti- 

 ficial dietary quite minute amounts of material extracted, 

 secundum artem, from animal or vegetable tissues and it supports 

 growth quite normally. 



It appears as though we shall have to extend our concepts 

 concerning efficiency in rations beyond the range of nutritive 

 values in the stricter sense and speak of the indispensable 

 "physiological actions" of certain constituents. Part of 

 dietetics is to become part of pharmacology ! 



I have avoided going into details with reference to this 

 matter, as others will follow me who are qualified to speak 

 concerning them. I have said enough to suggest that something 

 like a revolution is about to upset much of our dogmatic 

 teaching concerning animal nutrition. It is well, I think, that 





