SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 745 



weeded out, yet this was never the case. Again, a high population 

 of eggs would be very injurious, yet this was not so. Then it might 

 be supposed, if traces of oxygen were responsible, that admission of 

 air and re-evacuation would lead to further development, but this 

 was not the case. In atmospheres of 20 per cent, oxygen and 80 per 

 cent, hydrogen, the eggs developed just as normally as in the pure 

 hydrogen. Loeb supported Samassa's conclusions, working with 

 Ctenolabrus and Arbacia eggs. In atmospheres of hydrogen, he found, 

 development would stop, but by no means immediately; thus the 

 eggs of Fundulus (a bottom fish) could last 15 hours in complete 

 absence of oxygen, segmenting, and retaining perfect viability even 

 after 4 days' anaerobiosis. The eggs oi Ctenolabrus, on the other hand, 

 were very sensitive to carbon dioxide, and a stay of only 4 hours in 

 that gas killed them altogether. Arbacia and Paracentrotus eggs were 

 held up at once in the absence of oxygen, a fact subsequently con- 

 firmed by Warburg. Again, in later stages, the hearts of Ctenolabrus 

 and Fundulus behaved rather differently. In 10 mm. partial pres- 

 sure of oxygen the heart-beat of Ctenolabrus embryos was quite 

 abolished, but that of Fundulus embryos could proceed, if slowly, 

 for as long as 9 hours, and then completely recover. Carbon dioxide 

 was equally toxic for both hearts, and hydrogen would act as an 

 antidote to its action so that the heart might begin beating again 

 in hydrogen when that gas was substituted for carbon dioxide. 



O, Schultze opposed these conclusions. He maintained that the 

 technique of the other workers had been faulty, and that traces of 

 oxygen had been present. As a means of removing all such traces 

 from the air, he adopted the ingenious expedient of using the eggs 

 themselves. The eggs were placed in a tube (of just the right size to fit 

 them) passing through a cork. After 2 days, eggs Nos. i and 8 (those 

 nearest the open ends of the tube) were gastrulating, 2 and 7 were 

 beginning to do so, while Nos. 3, 4, 5 and 6 had all stopped in the 

 earliest cleavage stages. When all were turned out into a dish, however, 

 all developed normally. Schultze concluded that small amounts of air 

 must have been present in the other experiments, but it is as a matter 

 of fact very difficult to see from Samassa's account of them how this can 

 have been so. As for Loeb's results, Schultze interpreted them as being 

 simply due to a difference in oxygen requirement as between the two 

 embryos. Nevertheless, investigators continued to report confirmations 

 of Samassa's experiments, notably Godlevski in 1901, and contra- 



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