354 CARNEGIE INSTITUTION OF WASHINGTON. 



Recurring inquiries for information regarding the comparative 

 nutritive values of protein foods and requests for some graphic demon- 

 stration furnished the occasion for a series of illustrative feeding experi- 

 ments demonstrating the unique supplementary value of the proteins 

 of meat, milk, or eggs in enhancing the efficiency of some of the cereal 

 proteins for growth. A group of rats of the same age was fed on the 

 selected diets and after ten weeks the animals were photographed. 

 The series of illustrations thus obtained has aroused much interest 

 in the work. Those animals which had received rations the protein 

 of which was furnished by gliadin (from wheat) or zein (from corn) + 

 a little tryptophane, failed to grow; those which had received the total 

 proteins of corn grew a little only, whereas those whose diets had con- 

 tained two parts of protein from wheat-flour or corn-gluten feed, sup- 

 plemented with one part of protein from milk, eggs, or meat, grew nor- 

 mally and WTre very large, vigorous rats. At the end of four months 

 these animals were sent to the American Museum of Natural History 

 in New York, where they were stuffed and mounted. One set has been 

 returned to us, and the other placed on exhibition there as the nucleus 

 of an educational exhibit to which we expect to make additions from 

 time to time, and which will illustrate in graphic form some of the 

 fundamental principles of nutrition. 



The character of the nitrogen in leaves and other kinds of green 

 foods is a question not only of scientific interest, but also of economic 

 importance. Although during the early part of the last century the 

 presence of protein in green leaves attracted the attention of chemists, 

 attempts to study these were soon abandoned after it was found that 

 proteins could be so much more easily obtained from seeds. During 

 more recent years botanists have made observations on the proteins 

 in green leaves by micro-chemical methods, but no serious attempt, so 

 far as we can discover, has been made by any chemist to isolate and 

 study the proteins obtainable from such sources. Since green foods 

 and hays form so large a part of the nutriment of farm animals, we have 

 thought it essential to further progress in our scientific knowledge of 

 feeding animals to learn as much as possible respecting the protein 

 constituents of some particular leaf. We hoped thereby to develop a 

 method which might be applied to other kinds of leaves and thereby 

 ultimately increase our knowledge of the nutritive value of this class 

 of foods. 



Since spinach leaves contain nitrogen equivalent to over 30 per cent 

 of protein, estimated in the conventional way by multiplying by 6.25, 

 we have used these for our study. Only a small part of the nitrogen of 

 the fresh leaf is soluble in water, and much of this becomes insoluble 

 when the leaf is dried. The protein in these dried leaves show^s excep- 

 tional insolubility in the solvents usually employed for extracting 



