NUTRITION. 437 



subsist upon milk secreted by a mother living upon a diet deficient in a 

 factor which is essential for growth and which, it has been assumed, 

 can not be manufactured de novo by the animal. The effect upon the 

 offspring has been variable. In several cases the families of young 

 grew slowly and developed ophthalmia within a few weeks. In other 

 cases, the young appeared to be quite vigorous and grew fairly well. 

 We can not explain these differences in vigor until further investiga- 

 tions are made. It is interesting to note that the character of the diet 

 has affected the mother far less than the offspring. This is not easy 

 to understand in view of the presumable drain upon the maternal 

 vitamin resources during the period of lactation ; nevertheless it corre- 

 sponds with the frequently repeated observation that adult rats are 

 far less sensitive to a shortage of vitamin A in the diet than are younger 

 individuals. The uncertainty with respect to the yield of milk, or the 

 proportion which each one of a litter actually receives, is a formidable 

 obstacle to such investigations. 



The vitamin potency of cod-liver oil and products separated there- 

 from have been tested anew on animals failing upon diets free from 

 both fat and vitamin A. In several instances 14 milligrams daily 

 have sufficed to cure ophthalmia and in some cases to promote renewal 

 of growth. When cod-liver oil was ''fractioned" by a procedure similar 

 to that which we described several years ago in the preparation of 

 "butter oil," the vitamin A was concentrated in the more soluble frac- 

 tion ; the relative potency of such preparations is now being investigated 

 and renewed evidence of the unusual richness of cod liver oil in vitamin 

 A is being obtained. 



In agricultural practice corn or cornmeal frequently furnishes the 

 major part of the calories of the ration. The protein deficiencies of 

 maize are made good by the proteins of milk. The comparatively 

 high cost of the latter makes it important to use it in the most efficient 

 proportions. If skimmed milk is fed separately and before the corn- 

 meal, the animal may readily eat more than enough to supplement 

 properly the corn ; if fed milk after the corn, it may eat too little. The 

 proper way to feed these products, therefore, would be to mix them so 

 that both may be eaten at the same time. Such a method would be 

 particularly advantageous for those who have an irregular supply of 

 skimmed milk, because in this way all the latter would be used under 

 conditions of maximum efficiency. Furthermore, each individual 

 animal would get more nearly its proper quota of the milk. We have 

 found that mixtures of cornmeal and dried skimmed milk in which the 

 latter furnishes one-fourth of the protein of the food permit rats to 

 grow to full size, provided a small amount of suitable inorganic salt 

 mixture is added as a supplement. The experiments indicate that this 

 mixture of yellow cornmeal, skimmed-milk solids, and salts may be 

 sHghtly deficient in the fat-soluble vitamin. In practice such a mix- 



