SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 675 



dioxide output declined rapidly after the eggs had been taken from 

 the oviduct or had been laid, and by 100 minutes had reached a 

 steady low level. One thousand eggs 50 minutes after laying produced 

 upwards of 20 c.mm. of carbon dioxide per minute, but after the 

 looth minute was reached, their steady level was about i c.mm. 

 carbon dioxide per minute. McClendon's centrifugation experiments 

 already referred to showed that 16 per cent, of the frog's egg was 

 "clear and protoplasmic", 6 per cent, was fatty or oily and 78 per 

 cent, was yolk. As an average egg of Rana temporaria weighs 3-43 mgm. 

 (Bialascewicz & Bledovski), the amount of protoplasm in it would 

 weigh 0-55 mgm., or in 1000 eggs 550 mgm., and this amount at 

 I c.mm. carbon dioxide per minute (wet weight) would be o- 1 82 c.mm. 

 carbon dioxide per 100 mgm. protoplasm which compares inter- 

 estingly with Rapkine's 0-225 c.mm. carbon dioxide per 100 mgm. 

 in the sea-urchin's egg. But this calculation is not very significant, 

 owing to the manifold uncertainties involved in taking data from 

 many authors on different material in different conditions. It 

 does perhaps show a similarity between the metabolic rate of the 

 unfertilised egg of echinoderm and amphibian. The conclusion from 

 this part of Bialascewicz & Bledovski's work was that during life in 

 compact masses in the oviduct the eggs accumulate large quantities 

 of carbon dioxide, which has to be eliminated when the eggs are 

 brought into an atmosphere containing a much-diminished con- 

 centration of carbon dioxide. If this process were to go too far 

 fertilisation would become impossible, as Bialascewicz & Bledovski 

 showed by subjecting the unfertilised eggs to atmospheres of pure 

 carbon dioxide for as little as 2 hours, and these findings do indeed 

 go a long way towards explaining the phenomenon of prematuration 

 The average results for oxygen uptake and carbon dioxide produc- 

 tion of unfertilised and fertilised eggs worked out as follows : 



Carbon dioxide Oxygen used 



