Abstract
Since the completion of a previous study on the effect of pathogenic bacteria and bacterial toxins upon paramecia, 1 an investigation has been in progress on the effect of snake venoms and of toxins (tetanus, ricin and botulinus) upon protozoa. The recent appearance of Tunnicliff's related study with other toxins, 2 and particularly her consideration of the use of paramecia for determining the strength of antitoxins, has made advisable the recording of a preliminary report of the present investigation in so far as it is related to her findings.
In the study of the effect of tetanus and botulinus toxins, of ricin and of snake venoms upon protozoa, only the venoms have definitely given positive results. Crotalus atrox (Texas rattlesnake) venom,∗ in dilutions containing 0.00025 gm. per cc, had an immediate lethal effect upon Paramecium caudatum, Stentor coeruleus, Bursaria truncatella and Frontonia leucas. With Volvox spermatosphara and Oxytrichia fallax the venom was lethal in effect but very slow in action. The effect on Chilomonas paramecium was slight and only temporary while Coleps hirtus, Podophyra fixa, and Dileptus gigas were not affected.
A race of Paramecium caudatum has thus far lent itself well to and has given consistent results in measurements of the potency of snake venoms. The M.L.D. of Crotalus atrox venom for the race of Paramecium caudatum, in this case the least amount in one cubic centimeter of medium required to kill an animal in 24 hours, was 0.00002 gm. This was one twentieth of the least amount required to kill a 20 gm. mouse. The M.L.D. of Agkistrodon piscivorous (Mocassin) venom for P. caudatum was 0.0000014 gm., while for Bothrops atrox (Fer de lance of Central America) it was 0.0000125 gm. It is evident that the agent in these venoms that is principally responsible for the death of paramecia is thermolabile. It is hoped that further fractionation may make possible the study of the effect of each of the several constituents of venom upon protozoa.
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