712 



THE RESPIRATION AND 



[PT. Ill 



greater ventilation should be used, as too much was provided by the 

 embryo itself. Lamson & Edmond, using incubators of identical 

 form and a very large number of eggs, simply varied the ventilation, 

 the output of carbon dioxide from the eggs being sufficient as a 

 source. The results they obtained are best shown in the diagram 

 given in Fig. 150. The percentage hatch was never more than 85, 

 and seemed to be unaffected by the amount of carbon dioxide 

 present if it does not exceed 150 parts per 10,000; above that figure, 

 however, the hatch is much decreased, and when 500 parts is reached 

 falls as low as 14. Subsidiary experiments with added carbon dioxide 

 fully confirmed the results given. Rogalski has since studied the 

 details of this effect of carbon 

 dioxide on chick embryos. Lam- 

 son & Edmond were of opinion 

 that their tests demonstrated 

 diffusion rather than secretion of 

 gases to take place through the 

 allantoic membrane in the egg, 

 for, when the carbon dioxide in 

 the air was increased consider- 

 ably, that provided by the em- 

 bryos slightly decreased (ratio of 

 4-27 instead of 4-46). They also 

 confirmed the close relation found to hold by Bohr & Hasselbalch 

 between the weight growth curve and the increment curve of carbon 

 dioxide production. (Their weight figures are given in Appendix i.) 

 More directly physiological investigations were those of Atwood 

 & Weakley, whose values for carbon dioxide production in cubic 

 centimetres per egg per day are shown in Fig. 151. The technique 

 of these workers was very good, probably better than any of the others. 

 They regarded the ideal conditions to be 50 parts of COg per 10,000, 

 and gave a table showing the amount of ventilation in cubic feet 

 of air per 1 00 eggs per day necessary to maintain the concentration 

 of the gas at that level. In agreement with Bohr & Hasselbalch, 

 they found an initial output of carbon dioxide which was certainly 

 not coming from the embryo, but from the shell and the contents^. 

 Fig. 152, in which are placed some of their values for fertile and 

 infertile eggs respectively, demonstrates the kind of result they ob- 



^ See also p. 819 on this subject. 



Fig. 152. 



