66 
L. Kaufman: 
ence between the reaction of axolotls fed on thyroidine and those- 
fed on salicylic acid (both finally leading to the same effect) may 
be possibly due to the enzymatic character of the thyroidine food. 
We have to consider whether the changes which take place in 
axolotls fed on thyroidine might also be observed during normal 
metamorphosis in amphibians, i. e. whether the decrease of the re¬ 
spiratory organs is caused in both cases by the same factor. In the 
description of amphibians undergoing metamorphosis, decrease and 
emaciation of specimens during that stage is nearly always said to 
occur. The weighing of tadpoles undergoing transformation was done 
by S chap er and Romeis. From their investigations it is known 
that normally fed tadpoles diminish in weight considerably before 
metamorphosis. From the data given by Romeis it follows that 
this loss amounts to 17°/o °f the' initial weight and it occurs dur¬ 
ing a period of four weeks. A still more rapid decrease has been 
observed by Schaper; during a period of 9 days, between the 
formation of the hind limbs and the specimens 5 transformation into 
full-grown frogs, loss of weight in the tadpoles which he studied 
attained 54°/ 0 of initial weight. This loss is much larger than that 
of the amphibians subjected to starvation in Morgulis 5 experiments, 
where it amounted to 20‘8% (on an average) during 8 weeks; it 
corresponds to the decrease of weight which I observed in axolotls 
fed on thyroidine with meat. This is remarkable since the tadpol¬ 
es used by Schaper and Romeis, as well as my axolotls, were 
fed on meat whereas the amphibians experimented upon by Mor- 
gulis were subjected to total starvation. The following conclusion 
may thus be allowable: during the normal larval develop¬ 
ment of amphibians, at a certain stage a factor ap¬ 
pears having the same influence as thyroidine given 
as'food, and more intense than total starvation. 
The appearance of an internal factor which regulates the 
weight and chemical constitution of tadpoles during normal larval 
development was admitted by Schaper who maintains that some 
inherent cause induces processes of metamorphosis: „Die primä¬ 
ren Ursachen für alle diese Erscheinungen sind also 
im Inneren des Organismus zu suchen, oder mit an¬ 
deren Worten, nicht eine durch äußere Umstände be¬ 
dingte Inaktivität des Schwanzes und der Kiemen 
etc., oder eine herabgesetzte Ernährung sind àls aus- 
