3Q2 L. H. HYMAN. 



the oxygen consumption was found to rise continuously up 

 through late cleavage (determinations stopped at this point) ; 

 and in the eggs of Fundulus heteroclitus, up to the time when the 

 embryonic axis is established after which it fell, rising again 

 later apparently as the result of functional activity (unpublished 

 personal observations). Unfortunately in these cases, nothing 

 is known of the metabolic rate of the adult. Hasselbalch ( ! oo) 

 and Bohr and Hasselbalch ('oo) have measured the rate of 

 carbon dioxide production and oxygen consumption per kilo- 

 gram in chick embryos. Both were found to be very high in 

 the earliest stages determined five or six days, much higher 

 than those of the adult; the rates then fell rapidly. The carbon 

 dioxide output fell to the ninth day, after which it was about 

 contant, and about equal to that of the adult. The oxygen 

 consumption fell to the eleventh day, then rose again, and on the 

 sixteenth day was again considerably higher than that of the 

 adult. Bohr ('oo) compared the carbon-dioxide output of 

 guinea-pig embryos with that of the mother. He did this by 

 cutting open the uterus under anaesthesia, determining the 

 carbon-dioxide output of the mother and foetuses, then clamping 

 the umbilical cords of the foetuses, and again measuring the 

 CO 2 output of the mother. The difference between the two 

 measurements supposedly represents the carbon-dioxide pro- 

 duction due to the embryos. Of the six experiments of this kind 

 performed by Bohr, five showed the carbon-dioxide production of 

 the foetuses to be greater than that of the mother. The case 

 where the youngest embryos (5.5 grs. each) were encountered 

 gave a carbon-dioxide output very much higher than that of 

 the mother; the next size (16.5 grs. each) gave less CO 2 , but 

 still at a rate considerably higher than that of the mother; 

 while in the other four cases, with large foetuses, the CO 2 pro- 

 duction was slightly higher than that of the mother in three, 

 lower in one. 1 



1 I wish to state that the conclusions which I have drawn after careful perusal 

 of the papers of Bohr and Hasselbalch are somewhat different from those stated 

 by the authors. They conclude, curiously enough, that the respiratory rate of 

 the embryos of the hen and guinea pig is no higher than that of the adult, and 

 anyone reading their conclusion alone would certainly be misled. The authors have 

 either overlooked or ignored the fact, which their experimental data clearly show. 



