SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 729 



dioxide and used up 11-5 c.c. oxygen; a respiratory quotient of 0-913. 

 The following table gives the results obtained: 



Average (excluding 5 gm. embryos) 509 462 



A glance at the table shows that in all cases the respiratory quotient 

 was in the neighbourhood of unity, from which it may perhaps 

 be concluded, though Bohr himself refrained from emphasising it, 

 that the main source of energy in mammalian development is 

 carbohydrate^. During the periods when the maternal organism 

 alone was respiring, the respiratory quotients varied between 0-74 

 and 0-92, with an average of 0-84, instead of the foetal average 

 of 1-14. Perhaps most interesting of all are the figures for metabolic 

 rate, calculated on the basis of the carbon dioxide results. There is a 

 fairly close correlation as regards age, for the values run in order of 

 embryo weight, 1350 (this was regarded by Bohr as doubtful), 756, 

 252, 586, 462 and 488. The third of these is the only aberrant 

 one, and a first survey would conclude that the metabolic rate 

 declines in the guinea-pig embryo from a very early time, just as 

 it does in the chick. This point of view, however, does not fit in with 

 the data of the calorimetric workers mentioned below, and, as a 

 matter of fact, Bohr himself did not adopt it. He contented himself 

 with averaging the figures and concluding that the metabolic rate 

 in pre-natal life in the guinea-pig was of much the same order as 

 in the maternal organism, thus agreeing with Gusserov rather than 

 Pfliiger, and avoiding any commitment on the question of whether 

 during development it went up or down. Bohr's position was, of 

 course, that no true Entwicklungsarbeit was necessary, but that, at 

 the same time, the embryonic cells were not "in a condition to exist 

 without a vigorous metabolism". With his work all accurate in- 

 formation on the respiratory intensity and respiratory quotient of 

 the mammaHan embryo ceases, and there is probably no gap in our 



^ Again, Dickens & Simer found an R.Q,. of 1-04 for whole rat embryos in vitro 

 (see p. 703). 



47-2 



