amounts, with the exception of vitamin B which was lacking. 

 It had the following composition : 



Diet 94 



per cent. 



Casein - 18 



Butter fat 10 



Starch 68 



Salt mixture (Osborne and Mendel) 40 - 4 



Later, merely as a factor of safety, cod liver oil was substi- 

 tuted for one-fifth of 'the butter fat, making diet 107. The in- 

 gredients of the diet were weighed out and intimately mixed 

 first by hand and then transferred to a mechanical mixer and 

 stirred for five minutes. 



The casein was prepared from the commercial product 

 by purification in the manner suggested by Sherman and Husa 

 (unpublished experiments) as follows : One liter of 60 per 

 cent, alcohol (by weight) was added to 200 grams of casein 

 and the mixture stirred for one-half hour by means of a 

 mechanical stirrer and was then allowed to stand for five and 

 one-half hours. After this period the casein was filtered off 

 through a Buchner funnel and washed once in the funnel 

 with 500 cc. of 60 per cent, alcohol. The casein was again 

 treated with one liter of 60 per cent, alcohol as before but this 

 time was left to stand for eighteen hours. It was filtered off 

 and washed as before with 500 cc. of 60 per cent, alcohol and 

 finally with 500 cc. of 90 per cent, alcohol. The last washing 

 merely facilitates the drying. The casein was removed from 

 the filter and spread out in a thin layer and allowed to become 

 air-dry. Throughout this paper the strength of alcohol used 

 is always given in per cent, by weight. 



The butter was melted at a temperature not exceeding 

 45 C. All the curd, salt and water settles to the bottom of 

 the vessel and may be easily removed when the butter solidi- 

 fies. The butter fat is again melted at a low temperature, and 

 filtered through filter paper using a hot water funnel. 



The salt mixture described by Osborne and Mendel 40 

 was used. Commercially pure corn starch, which according 



8 



