SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 637 



first readings of Warburg's curve. The two curves show the oxygen 

 consumed and the carbon dioxide in c.mm. given ofT during the 

 fertilisation and early development of an amount of egg-substance 

 corresponding to 4-06 mgm. of nitrogen (approximately half a million 

 eggs) in the case of Echinus microtuberculatus. The respiratory quotient 

 for this experiment was 0-92. The lower line in Fig. 109 shows the 

 oxygen consumption of half a million unfertilised eggs (1-5 c.mm. in 

 10 minutes). The difference between this figure and the 56 c.mm. 

 of oxygen taken up in the same period immediately after fertilisation 

 is very striking. All the other graphs obtained by Shearer were of 

 the same form, from which it is evident that the uptake of oxygen in 

 the first minute is not only many times more than during any minute 

 before fertilisation, but also more than at any subsequent minute. 

 After the first couple of minutes the rate of increase of metabolic 

 rate falls off, and the curve ascends rather less steeply. The oxygen 

 consumption per unit weight (calculated on nitrogen basis) of the 

 unfertilised eggs per minute was found to be 0-15 c.mm., but the same 

 eggs fertilised consumed in the first minute after the addition of the 

 spermatozoa 12 c.mm. of oxygen, an increase of about eighty times the 

 former value. Shearer compared the respiratory rate of the eggs before 

 and after fertilisation with that of the liver of a well-fed cat (from 

 values in the literature) and obtained the following comparison : 



Respiratory rate 

 Cat liver ... ... ... 107 



Unfertilised egg ... ... 0-37 



Fertilised egg ... ... ... 13-8 



Now examination of sections of fixed material of Echinus eggs 

 during the process of fertilisation shows that the spermatozoa take 

 at least lo to 15 minutes to embed themselves in the cytoplasm of 

 the egg. In material fixed within 2 or 3 minutes of the addition of 

 spermatozoa to eggs the former are found only attached to the 

 external surface of the egg-membrane, not having had time to 

 penetrate it. Comparison of these facts, then, with the experimental 

 evidence, makes it clear that the initial burst of oxygen consumption 

 must be brought about simply by the first contact of the sperm with 

 the outside of the egg-membrane. The great rise in metabolic rate 

 which occurs in the very earliest stages of development cannot 

 depend on the formation of the male pronucleus in the cytoplasm, 

 and must be due to some activity exerted by the spermatozoon 

 before it has entered the egg at all. Moreover, when the fusion of 



