566 
Ill. A number of tadpoles being in a young stage of development 
(on April 30%) were put into a liquid, containing a quantity of 
uranium-salt and an aequiradio-active quantity of potassinm. In this 
liquid the tadpoles grew almost as quickly as the animals under 
control; on July 15 I already found one tadpole with front- and 
hind limbs; several other tadpoles soon get them as well; the smallest 
ones are 8—9 m.m. So these tadpoles grew more quickly than the 
uranium-tadpoles. 
It may be said, that as a general result of the experiments made, 
tadpoles in a medium containing a radio-active substance antagonistic 
to potassium, grow and metamorphose less quickly than in a medium 
only containing potassium. The food given to the tadpoles, is not the 
cause of this lingering, for in regard to the tadpoles in ordinary 
water, fed with rice, the uranium-tadpoles also remain backward 
in development. 
The first question that can be put is, if the tadpoles have taken 
uranium next to or instead of potassium. 
This question cannot yet be affirmed. From an investigation volun- 
tarily undertaken by Prof. Rincer, it appeared that no uranium could 
be demonstrated in the tadpoles. 
In another respect this experiment had a very important result 
though the percentage of potassium found in the tadpoles fed with pisci- 
dine, was in two cases 0.76 and 0.82 °/, from the dried tadpoles. The ura- 
nium tadpoles had evidently taken the minimal potassium quantity and 
even 0.91 °/, kalium was found. The potassium-perceniage was only 
0 49°/, of those tadpoles, which had been in water containing 175 
mer. UO, (NO,), and 50 mgr. KCl pro Liter (being aequiradio-active 
quantities). It here makes the impression that the presence of = 
aequiradio-active quantities of the antagonistic substances has thrown 
obstacles in the way of taking in potassium. Quite remarkable it is 
though that the concerned tadpoles should only stay little behind in 
growth to those, which had been normally brought up. *) 
The remaining backward in growth might be imputed to a 
possible poisoning caused by the uranium salt. 
In 1919 I have made a single experiment on this subject. On 
May 6'® I had five bowls containing 4 L. water each, and resp. 
0, 2*/,, 5, 7'/, and 10 mer. uranium-salt; every single bowl contained 
75 tadpoles as well; on June 19" resp. 51, 38, 24, 20 and 20 tadpoles 
1) Prof. Ringer fixes the attention on the fact, that the chemical investigation, 
viz. the investigation of the radio activity of the dried tadpoles, took place with 
so small a quantity of the dried tadpoles, that it is desirable this investigation should 
be repeated, namely about the absence of uranium. 
