Scientific Proceedings (60). 



"4 (93i) 



On the amino-acid content of involuting frog-larva. 



By Max Morse. 



[From the Physiological Chemical Laboratories, University of Wis- 

 consin.] 



In order to test the hypothesis that in the metamorphosis of the 

 larvae of the frog autolysis is the principal factor, estimation of the 

 amino-acid content was made by the gasometric method of Van 

 Slyke and by the formol titration method of Sorensen. Beckmann 

 freezing point and conductivity determinations were also made 

 since Bayliss, 1 Wells, 2 Sjoqvist 3 and others have shown that the 

 curve of proteolysis follows that of increase of conductivity and 

 lowering of the freezing point. 



Individual tadpoles were used at first, the tails being cut from 

 the bodies, dried in an air-blast at 40 0 C, pulverized in a mortar, 

 dissolved in water to make a one per cent solution, the estimations 

 being made upon the coagulable protein-free filtrates from boiling 

 with basic lead acetate. About 0.40 g. dried material could be 

 obtained from one individual, but this amount became in the 

 neighborhood of 0.10 g. in specimens which were absorbing their 

 tails. The determinations mentioned above gave no characteristic 

 differences between absorbing and non-absorbing animals. 



Attention was then directed to larger amounts and accordingly 

 the dried material from a number of larvae in the stages preceding 

 metamorphosis was mixed and another mass was obtained from 

 a number of individuals undergoing involution. The former gave 

 3.84 g. dried material, the latter 2.50 g. Upon these amounts, 

 determinations were made as above, but again no perceptible 

 differences in amino-acid content was found, nor were the freezing 

 point and conductivity determinations different in the two cases. 

 As typical examples, in conductivity experiments, with R = 500, 

 a — 58.1 for non-absorbing and 50.3 for absorbing; for freezing 

 points, D = 0.72 for non-absorbing and 0.73 for absorbing. For 

 formol titration with 20 cm. 3 aliquots, non-absorbing gave 0.1 



1 Journ. Physiol., Vol. 36, p. 221, 1907. 



2 Journ. Biol. Chem., Vol. 3, p. 35, 1907 . 

 3 Skand. Arch.f. Physiol., Bd. 5, p. 364, 1895. 



