III4 



PROTEIN METABOLISM 



[PT. Ill 



each set of readings, that it is impossible to interpret them, and useless 

 to present them. 



Table 153. 



A related form which has been investigated is the egg of the 

 plaice, Pleuronectes platessa, the nitrogen content of which was deter- 

 mined by Dakin & Dakin in 1925. Their table, 



Table 154. 



shows that, during the period preceding hatching, 78 mgm. of protein 

 are lost by this quantity of eggs, or 18-3 per cent, of the original 

 amount. In this tgg, therefore, the membranes must clearly resemble 

 those of the eggs of the anura rather than those of the eggs of the 

 salmonidae, in letting the products of protein combustion pass out 

 to the exterior. It is also obvious from Table 154 that the loss of 

 protein almost wholly accounts for the loss in dry weight, so that 

 between 80 and 95 per cent, of the total material catabolised must be, 

 in the case of the plaice, protein. The oxygen consumption (90 mgm. 

 per 2000 eggs), as found by Dakin & Dakin, nearly, but not quite, 

 equals that calculated from the lost protein, assuming that it was all 

 combusted. At the same time there is the 15 mgm. increase in fat 

 to be remembered. 



9-11. Protein Metabolism in Selachian Ontogeny 



With this we pass to the elasmobranch fishes. Little has been done 

 on the protein metabolism of their embryos, but it could have been 

 predicted beforehand that in this they would differ from other fishes. 



