SECT. 9] PROTEIN METABOLISM 1059 



Experiments of a somewhat similar kind were made by Sznerovna, 

 who took the proteins of yolk, white and embryo at different stages, 

 and hydrolysed them, effecting then a simple separation into di- 

 amine and mono-amino fractions. Her figures are given in Table 132. 

 They do not give any answer to the problem attacked by Plimmer & 

 Lowndes and by Russo, for she did not state the results for the massed 

 embryo and yolk proteins at the end of incubation, and they cannot 

 be calculated in the absence of information concerning the relative 

 weights of her i8th day embryos. Nevertheless her data for the 

 amino-acid distribution in the massed white and yolk proteins 

 strongly support the view that there is no intrinsic change in them 

 during development, for it is substantially the same on the i8th day 

 as at zero hour. On the other hand, her figures show a big difference 

 between the embryo protein of the 1 4th and that of the 1 8th day, 

 trending in a direction favourable to Plimmer & Lowndes rather 

 than to Russo. The mono-amino-acids in the embryo protein cer- 

 tainly seem to be diminishing, and the di-amino-acids to be increasing, 

 although such a change in the composition of the body protein 

 contradicts Cahn's suggestion of its constancy. The whole question 

 is confused, and needs further analysis than it has received. 



9-2. Metabolism of Individual Amino-acids 



Individual amino-acids, also, have been estimated in the hydro- 

 lysates of the massed egg-proteins at different stages of development. 

 Thus Abderhalden & Kempe in 1907 obtained the amounts of 

 amino-acids in the egg at o, 10 and 21 days, tyrosine by simple 

 crystallisation, glutamic acid by the hydrochloric acid method, and 

 glycine by esterification. In grams per cent, of the egg, none of the 

 three manifested any change, but the methods employed were not 

 delicate enough to settle the question. Levene was another pioneer 

 along these lines, but his data were few, and so erratic that no good 

 purpose would be served by discussing them. 



An important series of experiments on the metabolic behaviour of 

 individual amino-acids during incubation was carried out by Sendju. 

 Tryptophane in the embryo, the yolk and the white was estimated 

 by the von Fiirth colorimetric technique. As Fig. 295 shows, there 

 was a marked diminution of it in absolute amount throughout the 

 period, and this diminution took place in two stages separated from 

 each other by a plateau. Sendju identified the first of the two falls 



