NUTRITION. 307 



ence with some of them and their failure to promote the growth of 

 young rats. Much further work will be required before satisfactory- 

 answers can be obtained to the puzzling questions which these experi- 

 ments have raised. 



The study of the chemistry of the milk proteins has been continued; 

 for, strange as it may seem, our knowledge of this subject has been 

 limited. 



The coagulum obtained by precipitating casein from milk with acid 

 and heating the filtered serum has previously been shown to contain 

 two proteins, but concerning these the literature contains little that 

 is definite. We have separated these proteins from each other so 

 completely that the preparations did not react anaphylactically with 

 one another, and have determined their ultimate composition and 

 some of their properties. The individuality of these two proteins was 

 demonstrated by anaphylaxis experiments made by Professor H. G. 

 Wells. The phosphatides present in milk are associated with the 

 lactoglobulin, not with the pure lactalbumin. In its relation to the 

 phosphatides, lactoglobulin resembles the vitellin obtained from hens' 

 eggs and has little in common with most other globulins. 



The proteose, previously referred to in our earlier report, has now 

 been shown to originate largely from the other proteins of milk. 

 Whether any protein of this class is an actual constituent of fresh milk 

 has not been finally determined and can not be until better methods 

 are available for completely separating all of the other proteins. Our 

 experiments show, however, that the amount of proteose present in 

 fresh milk is, at the most, very small. 



We have already reported that we had isolated from the alcoholic 

 washings of large quantities of casein a considerable amount of a 

 hitherto unknown protein which, like gliadin from the wheat kernel, 

 is freely soluble in 50 to 80 per cent alcohol, but insoluble in absolute 

 alcohol and largely so in water containing more or less inorganic salts. 

 We have since studied this protein more fully. Toward solvents it 

 behaves quite unlike any protein of animal origin hitherto described. 

 It is distinct from all of the other proteins of milk, as shown bj^ the ana- 

 phylaxis reaction and the proportion of some of the amino-acids which 

 it yields on hydrolysis. That this protein is an original constituent of 

 milk and not a product of the action of alkali, or other reagents used in 

 purifying casein, is made almost certain by the fact that it is precipi- 

 tated together with casein simply by adding very dilute hydrochloric 

 acid to fresh milk. Owing to the fact that its acid compounds are sol- 

 uble in water, some also remains in the milk serum even after casein 

 has been precipitated by acid and the coagulable proteins by heat. 



Our report for 1917 mentioned the beginning of a somewhat elabo- 

 rate investigation of the role of the various inorganic elements in the 

 diet. This line of work has been continued with results which have 



