SECT. 4j HEAT-PRODUCTION OF THE EMBRYO 



711 



are used, but does if the eggs are fertile and developing properly. 

 Other factors which may increase it are the respiration of the hen 

 and the evolution of carbon dioxide from the soil. It never reached 

 a toxic concentration, however, although usually well above the 

 ordinary air of the room. 



400 



300 



CO2 production chick embryo 



O Bohr & Hasselbalch^ 



(l^''- series) ( / , \ 



^ ^ >(race unknown) 



® Bohr 8( Hasselbalch (^ ' 



(2"'^-series) j 



• Abwood &.Weakley.(White leghorn) 



® Murray ( » " ) 



e Hanan 



© Baumgarbner 



200 



100 



3 9 10 11 12 13 14 15 16 17 18 19 

 Fig. 151. 



Uncertainty about the action of carbon dioxide on development, 

 whether good or bad, had previously led to a good deal of work 

 designed to discover what proportion of the gas in the circulating 

 air gave the best results. Lourdel ; Brigham; Thom and Lamson 

 & Kirkpatrick advocated the addition of carbon dioxide to the air, 

 and Dryden; Edmond and Harcourt & Graham considered that 



N E II 46 



