648 



THE RESPIRATION AND 



[PT. Ill 



that, when the respiratory quotient is calculated, it begins just after 

 fertilisation at about unity (good agreement here with Shearer and 

 Warburg), but then rises to the extreme value of 4*0 at 4 hours of 

 development, after which it falls away to unity, and remains there 

 (due allowance being made for the influence of calcification) until 

 the pluteus stage is reached (see Fig. 115). Rapkine concluded from 

 this that the enormously high respiratory quotient of the 4th hour 

 indicated a period dominated by syntheses and in which a minimal 

 amount of combustion was proceeding. Coupled oxidation-reduction 

 reactions, the significance of which for embryonic development as 

 a whole will be dealt with in the section on Energetics, would here 



14 16 18 20 11 24 26 23 30 32 34 36 38 40 



Time in hours 

 Fig. 115- 



be proceeding to a greater extent than simple combustions, so that 

 the carbon dioxide put out would be out of all ordinary relation 

 to the oxygen taken in. Were this the case, the heat given out as 

 actually found calorimetrically would be smaller than that calculated 

 from the absorption of oxygen (endothermic reactions, which catch 

 and hold the heat for the organism, predominating), unlike the 

 state of affairs found to hold for the chick's later stages by Bohr & 

 Hasselbalch. Now Rapkine in a later paper calculated that this was 

 actually the case. Shearer found that, during the first 12 hours of 

 development in the sea-urchin, 25 1 -96 calories were given out, but the 

 heat corresponding to complete combustion of 31-3 mgm. of protein, 

 and 1-65 mgm. of fat (chemical analyses of Rapkine) amounted to 

 331-3 gm. cal. or half as much again. The discordance between 



