330 EFFECT OF CHEMICAL AGENTS [Ch. XI 



Additional experiments upon the frog's egg have been made 

 by Danilewsky ('95), who found that such eggs placed in 

 water containing y&too "^ lecithin gained in 54 days 300% 

 greater weight than those reared in pure water. The author 

 believes, however, that this small quantity cannot act in a 

 directly nutritive manner but, rather, that it favors in some 

 way the assimilation of food. 



Mammals. — The requirements of agriculture have led to 

 numberless experiments upon the feeding of domesticated mam- 

 mals. Yet they are for the most part of little value for our 

 purpose. A few of the better class of experiments from our 

 point of view may be given, together with such conclusions as 

 they permit. 



Years ago, Lawes and Gilbert ('53), from extensive feed- 

 ings of sheep and pigs, upon diverse foods, reached the conclu- 

 sion that those " apparently grew more where, with no defi- 

 ciency of other matters, the nitrogenous constituents were very 

 liberally supplied. Hence, the gross increase obtained might 

 be somewhat more nitrogenous with the large supply of nitrog- 

 enous food ; but it would in that case, according to some 

 experiments of our own, contain a larger proportion of water, 

 and less of solid matter, than where more fat had been pro- 

 duced." More recent studies made on various domesticated 

 animals tend to confirm these results. A mixed diet with an 

 abundance of nitrogenous food permits of greater growth than 

 an equal quantity of food of one kind, or mixed food in which 

 the nitrogenous constituent is scant. Growth tends to 

 increase with the quantity of nitrogenous food rather more 

 closely than with that of the non-nitrogenous food devoured. 



This conclusion is sustained by the striking results gained 

 by Pkosher ('97) in investigating the cause of the varying 

 percentage rate of growth of different mammals. The rela- 

 tion between growth and the percentage of the different 

 organic and certain mineral constituents of milk is given in the 

 following table : — 



