700 THE RESPIRATION AND [pt. iii 



"The oxygen may be", said Hasselbalch, "either a by-product of 

 syntheses associated with cell-division — possibly of fundamental 

 nature, analogous to the Og-assimilation of green plants, and 

 normally obscured by the mass of respiration — or on the other hand, 

 it may be purely a side-issue, originating from some fermentative 

 process or other associated with growth." And there is, as we have 

 seen, a third possibility. 



Brandes has more recently discussed the question afresh and regards 

 the oxygen given off by the yolk in Hasselbalch's experiments as of 

 much importance for the life of the embryo, cut off as it is from the 

 air by the thick shell and the mass of albumen. His remarks do not 

 include any chemical explanation of its origin but as we shall see 

 in Section 14-6 the yolk of the avian egg contains catalase in an active 

 condition and it is legitimate to suppose that the concentration 

 of hydrogen peroxide, activity of the enzyme, etc., may be so ar- 

 ranged that an appreciable part, if not all, of the oxygen require- 

 ments of the embryo during the first day or two, is provided for in 

 this manner. Brandes divides the respiratory life of the chick embryo 

 into the following stages : 



A. A "molecular" respiration of yolk-oxygen 



(i) without the presence of haemoglobin (i day), 



(ii) with the presence of haemoglobin (2nd to 19th day), 



(a) by the blastoderm circulation (up to the 6th day), 



(b) by the yolk-sac circulation (up to the 19th day). 



B. A respiration of atmospheric air 



(i) through the allantoic vessels (from the 5th day onward), 

 (ii) through the lungs (from the 1 7th day onward) . 



Brandes called attention to the old work of Dulk in this connection. 

 It is doubtful whether stress can be laid on the results obtained with 

 the technique of 1 830, but nevertheless it is interesting to recall that 

 the gas which Dulk obtained from whole eggs contained 6 per cent, 

 more oxygen than atmospheric air and, after 10 days' development, 

 li per cent. Bulk's work has already been referred to on p. 617. 

 His figures were: 



% oxygen 



Air 208 -2I-I 



Gas from whole eggs (o days) 25-26-26-77 



,, 5, (10 days) 22-47 (with 4-44 % carbon dioxide) 



,j ,, (20 days) 1 7-9 (with 8-48 % carbon dioxide) 



