SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



715 



able for this, but Fig. 142 shows that, as far as absolute values go, 

 Murray's curve corresponds with the slowly falling part of Bohr & 

 Hasselbalch's. Perhaps if Murray had ventured into the region 

 before the 6th day, he would have got higher points, and would have 



11 13 



Incubation age 

 Fig. 154- 



had to draw an S-shaped curve, as afterwards happened in the case 

 of oxygen. 



The only attempt that has been made to influence the metabolic 

 rate in the embryo is the interesting one of Hanan, who in 1928 

 injected doses of about 1/30,000 to 1/40,000 mgm. of thyroxin in 

 0-25 c.c. of dilute alkali into the air-spaces of developing eggs on 

 the 7th day of incubation. For about 5 days the injected eggs 



