SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 733 



maternal organism enters in as a disturbing factor. Much attention 

 has been given to the basal metabolism of women in pregnancy, and, 

 although the conclusions about the embryo are not too certain, it is 

 necessary to review them carefully. 



In 1908 Rubner expressed the belief that his surface area law 

 applied not only to the newly born animal but also to the embryo. 

 As the average weight of an individual human infant at birth is 

 8 per cent, that of the mother, Rubner calculated that the metabolic 

 rate of the foetus at term would be approximately twice the maternal 

 metabolic rate, but, because the foetus is not very active, its rate 

 would be less than that. Such a point of view agreed well enough 

 with the experimental values of Bohr. But it was very difficult in- 

 deed to know what part the new tissues would play in the total heat- 

 production of the mother plus the foetus as a unit, for, although the 

 embryo itself might have a much higher metabolic rate than the 

 mother, the fluids, the umbilical cord, the membranes, etc., would 

 have a very low one or none at all, while that of the placenta was more 

 or less incalculable. The earlier observations on pregnant animals, 

 moreover, gave conflicting results. Reprev could find no increase in 

 basal metabolic rate in the pregnancy of the rabbit, guinea-pig, and 

 dog, while, on the other hand, the figures of Oddi & VicarelH on mice 

 showed a marked increase. This increase was also found by Magnus- 

 Levy, who carried out the first reliable observations on a pregnant 

 woman; in this case the rate rose from 2-8 c.c. oxygen per kilo per 

 minute in the 3rd month to 3-3 c.c. in the 9th month (17 per cent.). 

 L. Zuntz however, did not find such a rise. Murlin in 1910 was able 

 to show that the extra heat-production during pregnancy in the dog 

 was almost exactly proportional to the number of embryos, i.e. the total 

 weight of the litter. The experiment was done on two pregnancies of 

 the same dog. The figures were as follows : 



Gram calories 

 produced per day 

 During sexual rest (normal) ... ... 505'3 



During first pregnancy ... ... 55 1 '3 



During second pregnancy ... ... 763-8 



In the first pregnancy i puppy was born, in the second 5. 55 1 "3 — 505-3 

 gave 46-0 cal. per puppy, or, as it weighed 280 gm., 16-4 gm. cal. 

 per 100 gm. Similarly 763-8 — 505-3 gave 258-5 cal., or 51-7 cal. per 

 puppy, or, as they weighed 3 1 2 gm. each, 1 6-8 gm. cal. per 100 gm. If 

 now it could be shown that the metabolic rate of the maternal organism 



