566 ON INCREASE IN COMPLEXITY [pt. iii 



day 3000 mgm. of total carbohydrate and about 100 mgm. of free 

 carbohydrate. After that point the total carbohydrate continuously 

 falls, reaching a value of 1750 on the i6th day, while the free carbo- 

 hydrate continuously rises, its highest point being reached on the 

 nth day with a value of 360 mgm., after which it falls, but not 

 below 220 mgm. We have therefore a considerable proportion 

 of the sugar present throughout not free and not in the form 

 of glycogen. It is very probable that this fraction can be called 

 "mucoprotein glucose", and that it is present in the form of com- 

 bination with a protein molecule. Its quantitative relationships are 

 interesting, for it amounts to 2550 mgm. per cent, dry weight on 

 the 5th day, but by the nth day it has fallen to about 1000 mgm. 

 per cent., after which it remains about steady at that level. No 

 stress is laid on the absolute magnitude of the figures, for the best 

 methods we have for estimating total carbohydrate almost certainly 

 give high results, but there is no reason for supposing that the relative 

 values are not significant. 



It seems that this behaviour can be correlated with facts that have 

 long been known to histologists. Von Szily was the first to describe 

 a cell-free connective-tissue or fibrous 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 Baitsell has recently 

 examined its properties with the aid of a micromanipulator. An 

 account of its comparative histology is given by Biedermann. It 

 appears to be secreted by the cells, and provides them with a homo- 

 geneous matrix, a kind of natural culture medium in which even 

 migration may take place if and when it may be necessary. As 

 development proceeds, the substance does not disappear, but be- 

 comes relatively less and less important in relation to the body as 

 a whole. The nearest equivalent to this ground-substance elsewhere 

 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 

 very rich in substances of the mucoprotein type, and the importance 

 of mucoprotein in the beginning of embryonic life leads inevitably 

 to a correlation with the jelly of von Szily. It explains, or is explained 

 by, the high proportion of combined glucose other than glycogen 

 at that period. This example is intended to give an idea of the kind 

 of correlation between chemical and morphological characteristics 

 which is necessary for the embryology of the future. 



