New York Agricultural Experiment Station. 493 



milk. Moreover, the construction of animal body fats from the 

 carbohydrates of the foods is now experimentally established be- 

 yond reasonable doubt. The investigations of Lawes & Gilbert, 

 Henneberg, Soxhlet, B. Schulze, Tscherwinsky. Chaniewski, E. 

 Voit, Lehmann, Munk and Rubner, show most clearly that with 

 sheep, pigs, geese and dogs the body fat accumulated could not 

 have come wholly from the protein and fats in the food eaten, 

 and, therefore, must have been formed in pan. at least, from 

 starch and similar compounds. 



It should be said, however, that neither these nor other experi- 

 ments demonstrate that food protein and fat may not take part 

 in the construction of body fat, but prove simply that carbohy- 

 drates do. The possibilities of food protein and fat in their re- 

 lation to fat formation in the animal body are not yet clearly un- 

 derstood. 



Concerning the sources of milk fat our knowhdge is less defi- 

 nite. The experiments of Boussingault, Voit, Wolff, G. Kuhn 

 and M. Fleischer are the ones that have been so far carried on for 

 the purpose of obtaining information upon this particular point. 

 The evidence which they furnish is entirely negative, because in 

 all cases the fat of the foods plus the possible fat from the meta- 

 bolized protein was, according to the interpretations of the sev- 

 eral investigators, wholly or nearly sufiicient to account for all 

 the fat in the milk. In fact, none of these experiments was so 

 planned or so long continued as to make safe conclusions possible. 

 Soxhlet has recently declared his belief that under certain condi 

 tions milk fat may in part be formed from body fat, but his con 

 elusion must be regarded as inferential, for he presents no ex- 

 perimental proof of his theory. 



It must be admitted that the production of milk fat involves 

 some conditions not pertaining to the formation of body fat. The 

 former is, according to the general concensus of opinion, the pe- 

 culiar product, like all other milk solids, of specialized tissues 

 called the mammary glands, the immediate location in these 

 glands of these particular metabolic changes being the epithelial 

 cers of the alveoli. A histological study of these cells when in a 



