386 Journal of Agricultural Research voi. xv, no. 7 



tions which they perform. Not only do they represent protein-saving 

 materials, since in their presence the animal organism needs less protein 

 for the maintenance of nitrogen equilibrium, but, a fact of still greater 

 interest, recent investigations have demonstrated that animals can be 

 maintained in nitrogen equilibrium, or even gain weight, when they are 

 offered completely digested protein or amino acids instead of unchanged 

 protein. This was shown to hold good for the organism of the dog (j), 

 and, generally speaking, undoubtedly holds true for the animal organism. 

 In this connection, it may not be amiss to mention that the various amino 

 acids perform special functions in the body. Thus, the amino acids lysin 

 and cystin have been recognized by Abderhalden (/), Osborne and 

 Mendel (52, 55, 54, 35, 36) as necessary for the function of growth, 

 and in this capacity can not be replaced by any other amino acids. 

 Equally, the diamino acids histidin and arginin (j, 2) are indispensable, 

 since when they are removed from a complete amino acid mixture (ob- 

 tained by protein hydrolysis), the remaining amino acids can no longer 

 maintain the body in nitrogen equilibrium. Glycocoll (j), on the other 

 hand, is not a necessary amino acid for the reason that it can be built up 

 synthetically in the animal organism. 



EXPERIMENTAL WORK 



The spinach materials used in this investigation were secured in part 

 from farms near Norfolk, Va.^ Since some of these spinach materials 

 (which were well mixed and treated as one lot) were not quite free from 

 aphids, it was thought advisable to obtain samples free from the insects. 

 These were taken from beds on another farm on May 6, 191 6.^ Three 

 kinds of samples of the diseased and healthy plants, respectively, were 

 prepared — namely, samples of the entire plant, of the tops, and of the 

 roots. The samples were first fumigated with a tobacco preparation, 

 then partly dried in the greenhouse for about a week, and partly in the 

 electric drying oven at 40° to 50° C. The dried materials were ground, 

 passed through a 40-mesh sieve, and kept in covered jars. As it was 

 very soon discovered that the moisture content of the materials was 

 changing, and also as it seemed more convenient to make practically all 

 of the experiments with air-dried spinach, care was taken to make the 

 ground spinach materials thoroughly air-dry. For this purpose they 

 were exposed to the air in thin layers, in a place free from dust, until 

 their moisture content became practically constant. The materials so 

 prepared were kept in sealed jars ready for use. The results pertaining 

 to the moisture content of the various spinach samples are expressed in 

 Table I. 



' By Dr. Rodney H. True, Dec. i, 1915, and by the senior writer Jan. 21, 1916. 

 * By Mr. J. A. McClintock, then with the Virginia Truck Experiment Station. 



