692 



THE RESPIRATION AND 



[PT. Ill 



this he deducted from the weight of the whole egg in his calculations 

 — it amounted to an average of 25 per cent., for the exact figures 

 see p. 322. The oxygen consumption expressed in cubic milhmetres 

 of oxygen per gram egg-contents per hour rose very steadily through- 

 out the incubation period, and this, of course, is exactly what was 

 found by the workers on the silkworm egg. It gives us no informa- 

 tion about the metabolic rate of the embryonic cells, and is simply 

 a reflection of the increase of organised living matter with corre- 

 sponding decrease of the non-respiring yolk. Melvin expressed dis- 

 agreement with Fink's hypothesis of the formative period in relation 

 to foliage eggs and earth eggs, and his results certainly do not support 

 it. He also made the interesting observation that temperature had 

 almost no effect on the respiration at the beginning of development 

 though it acted powerfully at the end. Thus a rise of 20° in the 

 external atmosphere gave a rise of o-oi mgm. oxygen per gram per 

 hour on the ist day of incubation and a rise of 1-92 mgm. oxygen 

 per gram per hour on the last day. 



4-10. Respiration of Reptile Embryos 



Only one investigation has been made of the respiration of the 

 reptilian egg. Bohr in 1904 worked on the snake. Coluber natrix, 

 from this point of view, having 

 been instigated to do so by 

 the results he had already 

 obtained on mammalian and 

 bird embryos, and by the re- 

 searches of Pembrey, Gordon 

 & Warren on the develop- 

 ment of heat regulation in 

 the chick. These snake's eggs 

 were developing under natu- 

 ral conditions in a heap of 

 leaves at a temperature of 

 about 29° and in an atmo- 

 sphere which, on examination, turned out to have only 47 per cent, 

 of oxygen and as much as 13-8 per cent, of carbon dioxide. Bohr 

 was able to incubate them artificially by keeping the air very humid, 

 though he did not attempt to reproduce an atmosphere of that com- 

 position. His figures are shown in Fig. 139 graphically. About three 



g;0-320 

 Z 0-310 

 g 0-300 

 2.0-290 

 "S 0-280 

 I 0-270 

 Z 0-260 

 f 0-250 

 '^0-240 

 8 0-230 

 0-220 



10 20 30 40 50 60 70 80 90 100 



Time, hours 

 Fig. 139- 



