634 Journal of Agricultural Research vci. x, no. 12 



He also states that there can be no doubt whatever as regards the 

 superior value of the proteins of meat, fish, eggs, and milk over those of 

 bread, beans, and Indian com. The proteins of rice and potatoes hold an 

 intermediate position. 



The difference in the efficiency of animal versus vegetable proteins is 

 further demonstrated by most wild animals in their natural selection of 

 food. It is well known that all wild animals of the cat species live alto- 

 gether on animal proteins. A recent investigation by the United States 

 Biological Survey (i) in regard to the character of the food consumed 

 by the wild birds of this country reveals the very interesting fact that 

 an average analysis of the contents of the craws of 14 species of wild 

 birds shows that approximately 50 per cent of all the food consumed in 

 a year's time consisted of animal matter in the form of insects. If the 

 fact that insects are only available for about six months of the year is 

 taken into consideration, it is to be assumed that the diet of the wild birds 

 consists almost entirely of animal protein during the season in which 

 insects are available. It is also to be noted in this connection that the 

 parent birds feed their young on a purely animal diet, thus exhibiting a 

 wonderful instinct in the selection of a food that is most efficient for the 

 rapid growth of their young. The avidity with which domestic fowls, 

 when allowed to range, seek insect food is familiar to all, and it is a well- 

 known fact that poultry thrive best when they have access to this kind of 

 food. 



After noting these phenomena in the selection of food by both wild and 

 domesticated birds, it is only natural to inquire whether there is any 

 chemical evidence as to the nature of the proteins contained in the 

 various insects which will substantiate the birds' instinctive selection of 

 this particular kind of food. 



Through the recent researches of Osborne and Mendel (3-5) of Yale 

 University and the Connecticut Experiment Station, it has been con- 

 clusively shown that the growth-promoting properties of certain proteins 

 are due to the presence of that kind of protein which is capable of yield- 

 ing upon hydrolysis the amino acids lysin, cystin, and tryptophane. 

 Then, if the instinct of the bird in its selection of its food is a true guide, 

 we would expect a protein analysis to show a considerable amount of 

 these growth-promoting amino-acid groups present in this type of food. 



In fact, protein detenninations made by the writer on two common 

 insects, the June bug (Lachnosterna sp.) and the grasshopper (Melan- 

 oplus spp.), showed such a large percentage of protein present in the dry 

 state that a further study of the character of the proteins present, as 

 revealed by the Van Slyke method for protein hydrolysis, was carried 

 out. The results obtained are shown in Table I, under the proper head- 

 ings, together with the results obtained by the same method of analysis 

 on a very tender piece of cooked beef roast and the cooked tender white 

 breast meat of a turkey. The specimens of beef roast and turkey were 



