180 The Feeding of AnimoJs 



interchangeable in the ration, without marked effect 

 upon its efficiency when the protein supply is not 

 diminished, it seems probable that the albuminoids are 

 largely interchangeable in use. On the other hand, 

 certain observed facts throw doubt on this view. For 

 example, w^ell- conducted experiments show that animal 

 protein is superior to vegetable protein as food for 

 ducks, when the two kinds are supplied in equally 

 digestible quantities. It is possible that there are 

 other differences in the effect of the protein from un- 

 like sources which the ordinary methods of observation 

 have not been competent to detect. 



One interesting question which has been consid- 

 ered, is whether the special nuclein bodies (albu- 

 minoids containing phosphorus) w^hich are found so 

 abundantly in eggs and in milk must be supplied as 

 such in the food, or whether they may be built up in 

 the animal from other albuminoids and phosphates. If 

 we could learn that the food must contain these pe- 

 culiar albuminoids all ready for use, then we would have 

 a valuable suggestion for feeding cows and poultry. 

 It now seems improbable that this is the case. The 

 sea salmon, which, during its stay up the river, is 

 believed to take no food, undoubtedly produces large 

 masses of eggs from the body substance, and it seems 

 unlikely that so much nuclein as is needed exists in 

 the flesh. If a cow gives thirty pounds of milk daily, 

 nearly or quite a pound of casein must come from 

 somewhere, and there is no evidence that any ordinary 

 ration would contain so large a quantity of phosphorized 

 albuminoids. Hens' eggs are rich in nuclein, beyond 



