296 1)1KTI;TIC' Dl'.FUIF.NtN'. 



certain .sul).stanccs mechanically or chemically associated with the 

 lipoid groti]). i^ives rise to dietetic insufficiency. 



So far back as 1881 Lnnin described experiments in feeding 

 mice upon a synthetic diet of caseinogen, fat, cane sugar, and the 

 ash of milk, and showed that, in si)ite of the abundance of l)oth 

 protein and n()n-])rotein in the food, the mice died 

 in from 20 lo 31 davs, whereas if fed upon simple 

 dried milk they were still aliv-e at the end of 2I2 months 

 In 1896 Hall carried out similar ex])eriments with similar 

 results; on the artificial diet the mice died within 40 days, 

 although they fed greedily at first. The experiments of Lunin 

 attracted considerable attention, and in the light of knowledge 

 current at the time were caj^able of explanation in several ways. 

 They established a marked difference between the dietetic efficacy 

 of dried milk, and a ration simulating it in all gross ])artictdars. 

 They did not. however, allow a decision to be made as to 

 whether the lacking factor Avas organic or inorganic. There was 

 no guarantee that the ash of milk supplied the necessary inor- 

 ganic constituents in suitable form of combination, wdiile on the 

 other hand, there was no evidence to show that any specific forms 

 of chemical combination within the mineral moiety of a diet were 

 necessary. 



R(">hmann in 1902 fed mice on so-called ])ure diets, but with 

 greater variation, and found that his animals remained healthv for 

 ^uuch longer i)eriods. Unfortunately his synthetic diets were far frtjm 

 pure, and his sitggestion that varioits proteins might vary greatly 

 in ntitritive value, although subsequently shown to be correct, 

 had ])robably no real Ijearing on his belief that the negative 

 character of the eaidier experiments on synthetic diets was due to 

 variation in the nature of the ])rotein fed. 



At this time very little was known concerning the true 

 nature of the deficienc\-, and Knapp. even in 1909. on the results 

 of experiments w'ith rats on a diet containing seven dfferent 

 varieties of j^ure proteins together with cholesterol, lecithin, car- 

 bohydrate, fat and salts, in which the animals died in from (j to 

 16 weeks, could offer no adecfuate explanation of the instifficiency. 

 He fiu'ther found that on a fat- free horse-flesh ration there was a 

 tendency to early death. This ol)scrvation is in accord with the 

 suggestion of .Stepp, made in the same vear, that the faihu'e to 

 maintain life on artificial diets was due to a lack of " lipoid "' 

 extractable from food bv organic solvents. Ste]j]> showed that 

 mice fed on milk bread thr(jve i)erfectly well, but that after 

 extraction with alcohol and ether the milk bread no longer 

 sufficed to maintain life, 'idie restoration of the extracted 

 lipoids t(j the extracted diet ])artially restored its maintenance 

 capacity, although comparison with controls on unextracted bread 

 suggested loss or destruction of some important lipoid constituent 

 during the process of extraction. 



Ho])kins in 1906 had alreadv suggested that certain materials 

 taken in the food v^ore essential to the organism without actually 



