IOI2 CARBOHYDRATE METABOLISM [pt. iii 



embryo. It is probable that none of the ovomucoid is combusted 

 during development, and the substance may therefore be considered 

 of architectural rather than of energetical significance. This is in 

 agreement with the main conclusion of Levene, who in his recent 

 monograph ascribes to the mucoids in general a structural, cementing, 

 and protecting value. From the ovomucoid curve in Fig. 269 we 

 should expect to find some clues for its significance in the embryo 

 about the 4th day and after the 1 1 th day, because at both these times 

 active ovomucoid catabolism is going on. And indeed it can be said 

 that at these two points the needs of two tissues are at a relevant 

 stage, namely, the primitive connective tissue and the bones. In the 

 formation of these mucoprotein will be required, as if for the inter- 

 stices of the growing embryo. 



Von Szily first described a cell-free fibrous connective tissue ground- 

 substance filling up all the cavities of the embryonic body in the 

 early stages. This has some affinities with the "cardiac jelly" of Davis, 

 and has recently been investigated by Baitsell, who has examined its 

 properties with the aid of a micromanipulator. It appears to be 

 secreted by the cells and provides them with a homogeneous matrix, 

 a kind of natural culture medium, in which migration may take 

 place if and when it may be necessary. As development proceeds the 

 substance does not disappear, but becomes less and less important 

 relatively to the body as a whole. The nearest equivalent to this 

 ground-substance in later life is the Wharton's jelly of the umbilical 

 cord and the vitreous humour of the eye. It is significant that both 

 these tissues are known to be rich in substances of the mucoprotein 

 type. It is probable that the decreasing importance of this primitive 

 connective tissue may be related to the decreasing percentage of 

 siUcon in the embryo (see Section 13), and perhaps it may have some 

 relation to the fall in the water-content of the embryo throughout 

 incubation (see p. 871). The amount of glucose in the embryo each 

 day not free and not present as glycogen can easily be ascertained. 

 Its gradual rise follows the growth of the organism. But if we express 

 it in percentages of weight of embryo, we find that 100 gm. dry 

 weight of embryo contain 2550 mgm. of "mucoprotein glucose" on 

 the 5th day, but only 980 on the 15th. This result is an interesting 

 comment on the suggestion that the importance of the primitive inter- 

 cellular matrix will require a high proportion of mucoprotein. 



The fall of ovomucoid in the latter half of incubation may be 



