SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 



697 



o CO2 (Bohr&,Hasselbalch1900) 

 ® ^^sUhasselbalch 1900) 

 • Cbj (Murray 1926) 



practically the adult level (Regnault) by half-way through the in- 

 cubation period, but Bohr & Hasselbalch's weighings were few in 

 number, and it would not be just to lay much emphasis on the 

 shape of the curve. That it descends so markedly, in opposition to the 

 ascending curves of the earliest stages in echinoderms and amphibia, 

 for example, is all that need at present be stressed. 



In the second paper Hasselbalch went on to investigate the oxygen 

 consumption of the eggs, and to calculate the respiratory quotient. 

 This last had only previously been approached by Baumgartner, 

 who, having found that i -63 litres of carbon dioxide were given off 

 during the whole of incubation, and that 1-76 litres of oxygen were 

 taken in, concluded that the 

 average respiratory quotient |s 

 was 0-93. Pott & Preyer's re- a^ 

 spiratory quotients had been f 

 obviously wide of the mark, ^^ 

 reaching in some cases 3-59. I3 

 Hasselbalch devoted a long a 

 preamble to the shortcomings >^ 

 of the earlier investigations, 5i 

 and first paid attention to the 8 

 growth-curve of the chick em- " 

 bryo, adding more figures to 

 those of Bohr & Hasselbalch, 

 which are given in Appendix i. He made measurements also of 

 the relation between the embryo and its membranes, and of the 

 water-content of embryo and allantois — these are mentioned else- 

 where in their proper place. 



Controls on infertile eggs showed that only an extremely small 

 amount of oxygen was taken up by eggs without living embryos, 

 not more than 0-15 c.c. per hour. A slight escape of nitrogen from 

 the eggs seemed to occur, but was very insignificant in amount. 

 Hasselbalch then went on to experiments with fertile eggs. The 

 oxygen consumption per hour followed the carbon dioxide output 

 closely, and rose in the same way as the weight curve, just as 

 Bohr & Hasselbalch had found to be the case for the increments 

 of carbon dioxide production. The respiratory quotients found 

 varied round about 0-7, but discussion of them will be deferred for 

 a moment. Hasselbalch found that, during the entire incubation 



45-2 



Tf-^-^-a ^ 



^ 



9 10 11121314 15 16 17 13 19 20 



Days of development 



Fig. 142. 



