On the amino-acid content of involuting frog-larvæ

Abstract

In order to test the hypothesis that in the metamorphosis of the larvæ 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 Sörensen. Beckmann freezing point and conductivity determinations were also made since Bayliss, 1 Wells, 2 Sjöqvist 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° 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 larvæ 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 cm3 aliquots, non-absorbing gave 0.1cm3, absorbing 0.3 cm.3 of n/5 Ba[OH]₂, in average of several determinations.