iio8 PROTEIN METABOLISM [pt. in 



development was, this value remained unaltered. In other words, 

 it is useless to attempt to alter the total amount of nitrogen wastage 

 associated with the making of one frog embryo by varying the 

 temperature, for all that will change will be the rate of the whole 

 process^. The following figures illustrate this: 



Hibbard has described in the anuran, Discoglossuspidus, the accumu- 

 lation and excretion of little superficial vacuoles in the epithelial cells 

 of the pre-hatching stages. These she regards as possibly the mechanism 

 of excretion of end-products prior to the formation of the kidneys. 



With the work of Gortner we pass to another aspect of the attack 

 on the protein metabolism of the amphibian embryo, although he 

 was concerned with an icthyoid urodele, Cryptobranchus allegheniensis 

 (the American giant salamander or "hell-bender"), and not with 

 the anura. In many respects his findings diflfer considerably from 

 those of the workers who have dealt with the latter material, and, 

 as Cryptobranchus eggs are very difficult to obtain, it is not likely that 

 he will be contradicted or confirmed very soon. Nevertheless, further 

 work would be desirable on this or a related animal, for Gortner 

 could find very little nitrogenous waste, and it is difficult to believe 

 that his figures for this are correct. He approached the subject from 

 the same angle as Plimmer & Lowndes, and, extracting the eggs and 

 hatched larvae first with ether and then with alcohol, he divided them 

 into what was soluble in ether and alcohol and what was not, which 

 latter residue he called the "protein" fraction. Then he determined 

 the different kinds of nitrogen in each. Table 150 shows his results. 



Taking the protein first, Gortner found that 100 eggs had 575-4 

 mgm. of protein nitrogen and 100 hatched embryos had 568-8, a loss 

 of 6-6 mgm., which he did not regard as significant. The character 

 of the protein in the eggs certainly differed from that in the embryos 

 at hatching, the main change being that, in the latter, the mono- 

 amino fraction had decreased and the di-amino fraction had slightly 

 increased. This finding agrees with the conclusions of Plimmer & 

 Lowndes on the hen's egg, and not with those of Russo. Slight rises 



^ Cf. Section 6- 10. 



