mo PROTEIN METABOLISM [pt. m 



would, he thought, appear as ammonia nitrogen. This, as Table 150 

 shows, rises in two fractions, from 0-048 to o-io8 per cent, of the total 

 nitrogen in the ether-soluble fraction, and from 9-956 to 10-21 per 

 cent, in the protein fraction, and remains constant in one, the alcohol- 

 soluble fraction. The total gain in ammonia nitrogen, namely, 

 0-314 per cent., would certainly not counterbalance the loss in mono- 

 amino-acids minus the gain in di-amino-acids, i.e. i -63 per cent. How- 

 ever, Gortner's conclusion that "no appreciable amount of urea or 

 uric acid is formed during embryonic growth in Crypto branchus" does 

 not follow, for the urea nitrogen may well have got mislaid among the 

 numerous other fractions, e.g. the non-basic nitrogen of the alcohol- 

 soluble fraction, which, in fact, does increase by 0-304 per cent. The 

 question cannot be regarded as settled until the same material is re- 

 investigated, using direct and modern methods for ammonia, urea and 

 uric acid. The gain in nitrogen of the ether-soluble fraction Gortner 

 interpreted as being due to a synthesis of lecithin such as Tichomirov 

 observed in the eggs of the silkworm. The gain in nitrogen of the 

 alcohol-soluble fraction he interpreted as being due to the synthesis of 

 purine and pyrimidine bases. 



As already mentioned, the loss of protein nitrogen was, per 100 

 eggs, 6-6 mgm., or 1-15 per cent, of the initial value, but the protein 

 itself, measured directly, fell from 4026 to 3828 mgm., i.e. 198 mgm., 

 or 4-92 per cent. Thus the protein at the end of development had a 

 distinctly higher nitrogen content than that at the beginning, being 

 14-86 instead of 14-3 per cent., and it is possible, as will be shown later 

 (see p. 1 178), that the missing material contributed to the production 

 of some synthesised fat. It must be remembered that it is not correct 

 to regard the hatching stage in amphibia (for Cryptobranchus see 

 B. Smith) as the end of embryonic development, for a considerable 

 period subsequently elapses before the yolk-sac disappears, and be- 

 fore the complete larval form is attained. As regards the question 

 whether any nitrogenous waste products are excreted into the water 

 while the embryo is yet in the egg, Gortner found the total nitrogen 

 to be practically identical at the beginning and at the end, being 

 584-9 mgm. and 584-5 mgm. per 100 embryos. It is probable, then, 

 that in Cryptobranchus little or no waste nitrogen is excreted into the 

 surrounding water before hatching, when what has accumulated is 

 discharged all at once, after which the animal can get rid of its end- 

 products without hindrance. The loss in dry weight amounted to 



