SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 723 



of 29-94 mm.). These findings agree well with those of Aggazzotti. 

 Hiifner himself carried out some experiments on the air-space contents ; 

 he was indeed the first worker to contradict the early assertions that 

 there was a much higher oxygen concentration within the air-space 

 than outside. His figures were: 



% carbon 

 % oxygen % nitrogen dioxide 



Hen 18-94 7997 i-og 



Goose 19-71 79-08 I-20 



He made an interesting calculation showing that the amount of 

 the gases which could diffuse in was much in excess of those actually 

 found. Baumgartner had stated that, on the 20th day of develop- 

 ment, a hen's egg gave off 0-56 gm. (285 c.c.) carbon dioxide and 

 took in 0-44 gm. (310 c.c.) of oxygen. Though the surface of the 

 goose's egg is only four times that of the hen's egg, Hiifner allowed 

 a ten times greater metabolism, but even so found that 3100 c.c. 

 of oxygen and 2850 c.c. of carbon dioxide stood much below the 

 182,700 c.c. of oxygen and the 43,460 c.c. of carbon dioxide which 

 his measurements would regard as being provided by diffusion. 

 However, Baumgartner's values are very low (60 per cent, of the real 

 values), and the multiplication of those of the hen by 10 to make those 

 of the goose is a hazardous proceeding, so the real gaseous factor of 

 safety of the hen's egg has not yet been calculated, and cannot be 

 until somebody repeats Hufner's observations on the shell of the hen's 

 egg. From some figures of Hufner's, however, for experiments in 

 which the inner membrane had been stripped off, a rough assess- 

 ment of this can be made in the case of the hen. Here in i second 

 at 9-4° and from a partial pressure of 159 mm. 1-587 c.c. of oxygen 

 would diffuse into the egg over all its surface (surface values being 

 taken from Murray), and the partial pressure being 29-94 mm., 

 0-554 c.c. of carbon dioxide would diffuse out. This would mean 

 137,000 c.c. of oxygen and 47,800 c.c. of carbon dioxide per day. As the 

 greatest amount of oxygen taken in is 720 c.c. per day, and the greatest 

 amount of carbon dioxide put out is 510 c.c. per day, there would 

 appear to be an ample margin. But 137 litres seems an immense 

 quantity of oxygen, and it is probable that Hiifner's figures are here 

 far too high; moreover, the inner shell membranes may probably 

 make a considerable difference. 



Another interesting point raised by Hiifner was whether the rates 

 of penetration of gases through the egg-shell followed Graham's law,^ 



