682 THE RESPIRATION AND [pt. m 



embryos, and such factors as alkali reserve, etc., were not exerting 

 too great an effect, then the Meyerhof theory is certainly more satis- 

 factory than the one suggested by Bialascewicz & Bledovski. But it 

 remains to be shown that absolutely all the carbon dioxide produced 

 was being successfully measured. That much fat is burnt during 

 amphibian development was definitely denied by Parnas & Krasinska 

 on the basis of their actual estimations of fat and protein during the 

 embryonic period, but this aspect of their work must be reserved 

 for discussion later. According to their view, the segmentation period 

 involves no more than a distribution among cells of protoplasmic 

 constituents already in existence in the egg, and it is not until the 

 separation of the embryo into the three germ-layers that intensive 

 chemical work begins to take place. It is this that leads to rise in 

 respiration. 



Frog's eggs, it seems, can be anaesthetised, and Irwin has studied 

 the consequent variations in their carbon dioxide output. 



4'8. Heat-production of Amphibian Embryos 



Only one examination of the heat-production of amphibian eggs 

 exists in the literature, namely, that of Gayda, who described a 

 differential microcalorimeter of great accuracy which could be 

 used for small objects. With this instrument he measured the heat- 

 production of the eggs of the toad, Bufo vulgaris, throughout their 

 development from fertilisation to hatching. Ruffini had previously 

 ascertained that small amounts of water in which the eggs of Bufo 

 vulgaris were developing had usually a temperature of from 0-5° to 

 0-6° at 10° and from i-o° to 1-5° at 20° higher than control quantities. 

 Gayda confirmed many other workers on other material by finding 

 that the heat-production did not rise pari passu with the increase in 

 nuclear material or in number of blastomeres. Fig. 133, taken from 

 Gayda's paper, shows the curve which he constructed from all his 

 average results, where gram calories of heat evolved per gram of 

 embryo and larva per hour is plotted against time, i.e. days from 

 fertilisation. The arrow pointing downwards marks the point of 

 hatching, and towards the 120th day metamorphosis begins. The 

 shape of the curve is very regular and striking. Rising smoothly 

 from the moment of fertilisation, and so continuing unaffected 

 by the hatching process, it reaches a blunt peak at about the 



