326 THE VITAMINES 



concluded that rickets in dogs is not dependent upbn the lack of 

 antirachitic vitamine, but upon the energy content of the diet, 

 exercise and hygiene. However, they admit that dogs on skim- 

 milk develop rickets more readily. 



Hess and Unger (I.e. 96), in particular, have subjected Mellanby's 

 results to a sharp scrutiny. .They maintained five children, 5 to 

 12 months old, on a diet composed of 180 grams Krystalak (dried 

 skim-milk with 0.2 per cent fat), 30 grams cane sugar, 15 to 30 grams 

 aufcolyzed yeast, 15 cc. orange juice and 30 grams cottonseed oil 

 (cereals for older children). Some of these children were kept for 

 several months on this diet, and as they grew older the amount of 

 cereal was increased, no other change being made. At the time of 

 publication, the diet was thought to be completely free of vitamine 

 A. These remarkable experiments showed for the first time that 

 vitamine A as it occurs in milk plays only a minor part in the develop- 

 ment of rickets. This finding, which contradicts somewhat the 

 results obtained by Mellanby in his experiments on dogs, was not 

 generally accepted. Hopkins (I.e. 595) held it against Hess' experi- 

 ments that the above diet was not entirely free from vitamine A, 

 since skim-milk may still contain this substance; cottonseed-oil too 

 is not free from this vitamine. Although these objections are 

 partially justified, we can not doubt that the dietary used by Hess 

 and Unger was indeed very poor in vitamine A. The favorable 

 result obtained with this diet, extremely poor in vitamine A, suggested 

 that the diet per se is not the only causative factor in the etiology of 

 rickets, and that there are still other factors to be taken into consider- 

 ation. Should they be so interpreted, that rickets has nothing to do 

 with vitamine A, as Hess and Unger naturally concluded at first? 

 On the contrary, these important experiments show that under 

 certain conditions, the vitamine A requirements of children may be 

 very slight, namely, when the composition of the diet as regards 

 protein, salts, vitamines B and C leaves nothing to be desired. The 

 individual differences in children on the same diet may perhaps be 

 attributed to unequal utilization of dietary constituents, a point 

 which has not been allowed for in the experiments of Hess and Unger, 

 or to the influence of light, which was entirely disregarded in 

 all their earlier experiments. In addition Hess and Unger reported, 

 that they observed rickets in children fed on milk (600 to 700 cc. 

 daily) containig 2.5 to 3 per cent fat, and also in breast-fed 



