THE FERTILISATION OF THE EGG 175 



Favourable material is naturally provided by animals which 

 spawn into the water eggs which contain relatively little yolk ; 

 and the eggs of marine animals are best for this purpose, the 

 physico-chemical equilibrium being in such cases of a more 

 mobile character. From the rapid advances made of late 

 years in the technique of tissue-culture it would not seem 

 unlikely that the initiation of developmental stages without 

 contact with sperm will be accomplished in our own time in 

 mammalian ova. 



In the Echinoid egg, which up till now has yielded the most 

 satisfactory material for experimental manipulation, an im- 

 portant aspect of the union of the sperm and egg is the 

 immediate increase in oxygen consumption which occurs 

 after entry of the sperm. At an early stage in the study of 

 this problem, Loeb suggested that the immediate effect of 

 the penetration of the sperm might be to promote a series of 

 oxidative processes. Warburg's (1908) determinations of the 

 oxygen-consumption of fertilised and unfertilised eggs of 

 Arbacia confirmed Loeb's prediction. Warburg found that 

 a quantity of eggs (about four million) in sea water, equivalent 

 to 28 mg. total nitrogen by the Kjeldahl estimation, took up 

 4-5 c.c. of oxygen during the first hour after insemination, 

 while only about o'5-o*7 c.mm. were consumed by the un- 

 fertilised egg in the same time. Warburg's original experi- 

 ments were carried out by a titration method (Winkler) ; in 

 later ones the manometer was used for the gas analyses ; and 

 readings of the rise in oxygen consumption were not taken 

 till ten minutes after fertiUsation occurred. From the recent 

 observations of Cresswell Shearer (1922), using the Barcroft 

 differential manometer, there emerges the remarkable con- 

 clusion that the mere contact of the spermatozoon with the 

 external surface of the egg is capable of increasing the oxidation 

 rate of the latter by rather more than 8000 per cent, in the space 

 of one minute. The eggs were fertilised in the chamber of 

 the manometer, so that there was no interruption of the readings 

 before and after fertiUsation. Within a minute of the libera- 

 tion of the sperm the increase in oxygen-consumption starts, 

 but it takes more than two minutes for the sperm to penetrate 



