SECT. 8] 



CARBOHYDRATE METABOLISM 



[051 



8-12. Pentoses 



This type of compound has a certain importance in relation to the 

 development of the nucleic acids of the embryo, since Calvery has 

 shown that, besides the ordinary hexose nucleic acid which occurs in 

 animal tissues, the chick embryo possesses also a pentose nucleic acid 

 not unhke that of plants. The only investigation of the pentose- 

 content of an egg is that of Mendel & Leavenworth, who estimated 

 it in hen's and duck's eggs, using Tollens' method. Their figures are 

 shown in Fig. 291, from which it is obvious that the pentose-content 

 of the eggs rises, reflecting the increase in nuclear substance. 



8-13. Lactic Acid 



A good deal more is known about the metabolic behaviour of 

 lactic acid in the hen's egg. It 

 was first found there by Bon- 

 nanni in 19 14, who regarded it 

 as a normal constituent and re- 

 ported more in the white than 

 in the yolk. He stated that the 

 fresher the egg the more lactic 

 acid it contained, that there was 

 less in the winter than in the 

 spring, and that by feeding 

 sajodin to hens the lactic acid 

 content of their eggs could be 

 raised. Anno next found traces 

 in the hen's egg-white before 

 incubation, and a rise to the 

 4th day, but none in the yolk 

 and no rise. Tomita estimated 

 it each day during incubation, 

 and his data are plotted in Fig. 292. An extremely sharp peak is 

 to be seen in both yolk and white on the 5th day of incubation. 

 Tomita drew attention to the coincident marked fall in free glucose, 

 which he knew only through the work of Sato, and expressed the 

 belief that the two phenomena were intimately associated. Perhaps 

 the mechanism by which the lactic acid is transformed into some 

 other compound is itself in course of development, and does not 

 increase in activity as fast as the mechanism which produces lactic 



Fig. 292. 



