SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 743 



of oxygen was used, the difference was unmistakable, for cells from 

 lo-day old embryos would not grow at all, while those from 5-day 

 old embryos grew excellently. Wind also made the very interesting 

 observation that, if the cells were in each case sub-cultured for many 

 weeks and then brought under anaerobic conditions, the difference 

 between the cells from lo-day embryos and those from 5-day 

 embryos had entirely disappeared. No difference in growth was 

 now perceptible. 



Work along these lines was continued by Wright whose results may 

 be summarised in the following table : 



Table 86. 



Mm. mercury 



pressure of 



oxygen 



Wright Explants of loth day chick embryo myoblasts: 



(a) In 0-22 % glucose : mitosis ceases at 



emigration ceases at 



(b) In o-o6 % glucose: mitosis ceases at 



emigration ceases at 

 ,, Jensen rat sarcoma: mitosis ceases at 



,, Mouse carcinoma: mitosis ceases at 



Ephrussi, Chevillard, Explants of 8th day chick embryo heart fibroblasts : 



Mayer & Plantefol mitosis (but not movement) ceases at ... ... y-o 



These facts lead naturally to the consideration of the evidence 

 which has been brought forward from time to time in favour of the 

 view that during the early stages of embryonic development anaero- 

 biosis may be possible, or may even normally occur. There is no 

 need to dwell on the first efforts of the workers on the hen's egg, 

 for their experiments have already been briefly described. Nor can 

 cleavage of echinoderm eggs go on in the absence of oxygen. Some 

 recent careful experiments of Amberson on the eggs of Arbacia punctu- 

 lata have demonstrated that cleavage proceeds at normal rate down 

 to very low oxygen tensions — about 1 1 mm. of mercury, between 

 which point and 4 mm. the rate is slowed down, while below 4 mm. 

 cell-division in this egg will not go on at all. Drastich finds exactly 

 parallel effects in the case of Strongylocentrotus lividus. In the case of 

 the nematodes, again, Zavadovski showed in 19 16 that cleavage in 

 Ascaris megalocephala would not go on in the absence of oxygen and 

 that the reason why it stopped in putrefying media was because the 

 bacteria were successfully operating a prior claim for the oxygen present. 

 More recently, Zavadovski & Orlov have demonstrated the absolute 

 dependence of many nematode embryos on oxygen for their cleavage, 



