742 



THE RESPIRATION AND 



[PT. Ill 



4-17. Anaerobiosis in Embryonic Life 



Very few observations have been made of the respiration of em- 

 bryo cells in tissue culture, but Burrows has some interesting experi- 

 ments in this direction. Taking explants of chick embryonic heart 

 cells, he placed them in different partial pressures of oxygen, and 

 found that their behaviour was quite different according to the stage 

 of development of the chick from which they had been taken. The 

 results he obtained are pictured 

 in Fig. 167, from which it can 

 be seen that fibroblasts from 

 4-5-day embryos would grow 

 and pulsate for 46 hours or so in ^^ 

 pure nitrogen, and for 50 hours 

 in only 7-5 per cent, of oxygen. 

 Fibroblasts from i o- 1 5-day em- 5 30 

 bryos, however, would not grow 8 

 at all in nitrogen, and only for -^ 

 12 hours in 1-5 per cent, oxy- °2o 

 gen. Burrows was in doubt as 

 to the meaning of these pheno- 

 mena, but explained them by 10 

 the hypothesis that there must 

 be some source of energy con- 

 tained in the young cells, which 

 the older ones have not got. 

 One is reminded, on the one 

 hand, of the work of Cohn & 

 Murray on the growth-rate of embryo explants, and, on the other 

 hand, of the concept of "ontogenetic momentum" which Byerly's 

 results on asphyxiated embryos (see p. 607) and de Bruyne's results 

 on embryo autolysis (see Section 14-11) have brought into being. 

 Consideration of it will be postponed till later in the book. Burrows 

 found, in a word, that with age the property of being able to 

 grow anaerobically declined, and was eventually lost. This im- 

 portant result was fully confirmed by Wind, who modified it by 

 using really strict anaerobic conditions. Under these only the very 

 slightest amount of growth went on even with heart-cells from 4-5- 

 day old embryos, but when an atmosphere of 2-10-* vol. per cent. 



10 15 



Days of development 



Fig. 167. 



