SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



769 



of the heart (dry) rose from o-i to o-8 mgm., so the N.G.R. fell from 

 about 50-25 to 14. It is interesting to note that, in their figures 

 for tissue cultures of fibroblasts, the R.R. and the N.G.R. were both 

 systematically higher the fewer the number of sub-cultures that had 

 been gone through since the tissue was first explanted. Perhaps this 

 might be regarded as evidence 

 that with increasing age the 

 metabolic rate declines in tissue 

 culture, just as the growth-rate 

 does, as was shown by Cohn & 

 Murray (see p. 461 and Figs. 

 62 and 174). 



Work on embryo tissues was 

 further extended by Kumano- 

 mido, who studied the respira- 

 tory metabolism of chick em- 

 bryos in chick serum and in 

 Ringer solution. The N.G.R. 

 was in all cases some 50 per 

 cent, higher in the latter than 

 in the former. Kumanomido 

 felt able to conclude that this 

 difference was not due to a 

 cytolysis or other injury effect 



40 

 OH 



o 



30 



1 2 3 4 5 6 7 8 3000 



No.of times the fibroblasbs were subcultured 



Fig. 174. 



in Ringer, but to an inhibiting effect of serum, owing to which the 

 maximum intensity of lactic acid production was not reached there. 

 Dialysis of the serum so that most of the salts and crystalloidal sub- 

 stances disappeared did not affect its depressant property, nor did 

 heating for 30 minutes at 55°. Kumanomido did not state, however, 

 whether these conclusions applied to the O.G.R. as well, but it would 

 be important to know this, in view of Negelein's results on rat em- 

 bryos, where there was a measurable O.G.R. in Ringer but not in 

 serum. Fig. 175, taken from Kumanomido, shows the decline in 

 N.G.R. with age during incubation in the chick embryo. This graph 

 is directly comparable with that of Negelein for the pre-natal life of 

 the rat, shown in Fig. 1 69 and with that of Rosenthal & Lasnitzki 

 for the developing liver and kidney of the rat shown in Fig. 1 76. 



The extent of the fall in anaerobic glycolysis rate does not seem 

 to be so great in the chick as in the rat, for in the former the drop 

 is from 27 to 10, and in the latter from 35 to 5. But Kumanomido's 



