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A NOTE ON THE USE OF THE SOUTH AFRICAN CLAWED 
TOAD IN THE BIOLOGICAL ASSAY OF THE DIGITALIS 
SEE1ES. 
By J. W. C. Ounn. 
The clawed toad, Xenopus laevis, is the most common batrachian in 
laboratory use in South Africa. Morphologically it is most closely related 
to the toad, but it is active in its movements like the frog, and there is some 
evidence that its electrical responses are at least as quick as those of liana. 
Yulpian (1) was the first to state, and his observations have been 
repeatedly confirmed, that the European toad has a considerable degree of 
natural tolerance for poisons of the digitalis series, the minimal lethal dose 
for the toad being several times greater than for the frog. Abel and 
Macht (2) have shown the same to hold true for the tropical toad, 
Bafo agua. 
It is therefore not only of scientific interest to determine whether 
Xenopus reacts to digitalis bodies like Bufo or Bana, but also of practical 
importance, since the most convenient method of standardising preparations 
of digitalis is to determine their toxicity for the frog. 
Method. 
The method employed was that in common use in biological assay of 
digitalis preparations. A measured quantity of the drug was made up to 
•5 c.c. with Singer's solution and injected through the floor of the mouth into 
the ventral lymph-sac of the toad. Freshly caught animals were used. 
Either the minimal lethal dose or the amount required to arrest the 
ventricle in systole in one hour (the minimal systolic dose) was estimated. 
The room temperature varied between 21° and 23° C. 
Minimal Lethal Dose of Strophanthin. 
The strophanthin used had been tested on Bana temporaria in the 
Wellcome Physiological Research Laboratories and the minimal lethal dose 
found to be about 0*0008 mgrm. per gramme weight of frog. 
