SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 639 



There is no need to suppose that the "Atmungsferment " is con- 

 centrated in the cortical layers of the egg, for in a protoplasmic 

 system the transmission of a physical change would readily occur 

 (see also p. 867). 



Shearer also carried out some experiments on the glutathione 

 content of the eggs before and after fertilisation. He stated that, 

 before fertilisation, they only gave a weak nitro-prusside reaction, 

 but that, immediately after fertilisation, deep magenta colours could 

 be obtained by this test, indicating the presence of reduced gluta- 

 thione in some quantity. "There seems to be fairly substantial ground 

 for believing", he said, "that there is an immediate increase in the 

 quantity of this remarkable body in the ovum on fertilisation." 

 Work with the nitroprusside test, however, must be interpreted 

 with caution until quantitative estimations of glutathione have been 

 done on the early stages of the developing echinoderm egg by the 

 iodine method or by some other suitable technique^. 



As regards the great initial rise in metabolic rate in the first 

 minute of the experiment, there is every probability that it represents 

 the results of egg-oxidations. But in view of the recent work of Gray, 

 this cannot be said to be a certainty, for Gray, examining the respira- 

 tion of spermatozoa, finds them to have a much larger and more 

 variable metabolic rate than had been suspected by the earlier 

 workers. Warburg's original figures relating spermatozoa oxygen 

 consumption to egg oxygen consumption were obtained in very con- 

 centrated sperm suspensions, and Gray has been able to observe much 

 higher rates of oxidation, especially during that period of activity 

 which the spermatozoa go through just before the eggs are fertilised. 



Other and less important measurements have been made of the 

 oxygen consumption of echinoderm eggs before and after fertilisation. 

 Thus McClendon & Mitchell in 19 12, using the Winkler method, 

 demonstrated a rise of six to eight times the previous value at fer- 

 tilisation, whether natural or parthenogenetic, in the case of Arbacia 

 punctulata. McClendon's theory was that fertilisation led to permeability 

 changes in the eggs which permitted a greater volume of gas to pass in 

 and out per unit time. 



As will be seen later, Meyerhof made a good many estimations 

 of oxygen consumption during the early stages of development of 

 the sea-urchin's egg, in connection with his researches on the calorific 



^ Rapkine's more quantitative experiments indeed show a diminution of SH on 

 fertilisation followed by a rise to the time of first cleavage. 



