alsberg: biochemical analysis of nutrition 279 



Animal feeds consist in the main of vegetable proteins which 

 are often incomplete. Obviously such a feed can be used most 

 economically if it is supplemented by small amounts of pro- 

 teins which supply the missing elements. To do this it is neces- 

 sary to know what amino-acids are contained in the different 

 vegetable foods. Agricultural chemists are now engaged in 

 studying this problem. In this connection it must be pointed 

 out that there is a distinction between maintenance and growth. 

 It is perfectly possible to maintain an animal in good health 

 upon a diet which will not permit it to grow. It is possible to 

 stop the growth of an animal by putting it upon such a diet. 

 When the diet is changed growth may be resumed. The capacity 

 for growth has not been destroyed. Furthermore, it has been 

 shown that it is not safe to conclude that a given diet is sufficient 

 if it permits an animal to develop to adult life. It is necessary 

 to show that it will also permit it to reproduce. There are 

 diets that apparently permit perfect development but do not 

 permit reproduction. It has also been found that more growth 

 will take place upon a diet containing a mixture of incomplete 

 proteins than upon a diet containing only one or two of them. 

 Thus growing pigs will utilize for growth only about 24 per cent 

 of the proteins of corn or wheat, whereas upon a mixture of 

 the two grains they will utilize for growth about 33 per cent. 

 It may be stated by way of comparison that pigs will utilize 

 for growth about 60 per cent of the milk proteins fed. 



Some of the investigators who put animals upon these restricted 

 diets found that the animals throve a great deal better if small 

 quantities of certain substances were added to the diet. The 

 presence of so small a quantity of milk that its protein was a 

 negligible factor kept animals growing or in good condition 

 upon diets that would not otherwise permit the animals to 

 remain in good health. A diet which does not permit normal 

 growth will do so if a small quantity of butter is added. Appar- 

 ently there are present in certain foods small quantities of 

 substances of unknown nature which are necessary to growth 

 and life. What this substance in butter is is not known. It 

 seems to contain neither nitrogen nor phosphorus. This is 



