Abstract
I. In our previous paper 1 we were able to show that the influence of ultraviolet radiation on P. caudatum can be expressed by the Arndt-Sehultze's law. Since the body of P. bursaria is full of green symbiotic algae, it seems worth while to compare the susceptibility of 2 species of Infusoria, differing in body coloration and hence in absorption of radiation.
2. As a source of light was taken a quartz mercury vapour burner of Hereus Hanau, 110 volts of alternating current and 6-7 amp. at a distance of 35 cm. from the animals under quartz Petri dishes filled with water 0.5 cm. deep. The control animals were put under glass dishes to absorb the ultraviolet part of the spectrum. An oatmeal medium containing Bacillus subtilis was used. The first series consisted of 5 separate experiments of about 160 specimens each. After keeping them for 24 hours at a temperature of 25°C. on slides with hollows their progeny were counted. The second series of experiments consisted in submitting the same cultures to repeated radiations on consecutive days, keeping the number of parental animals equal to 192. The number of the progeny of each specimen in the first series was expressed in per cent of the average number of the progeny of the control of the corresponding experiment.
These data show that a radiation of 40 seconds produces in P. caudatum a depression of the division rate and the zone of stimulative action is therefore located between 0 and 25 seconds. The curve for P. bursaria goes above that of P. caudatum and correspondingly the zone of stimulation is extended more to the right somewhere between 0 and 80 seconds. On the whole P. caudatum is about 2 times more susceptible to the stimulative and depressive action of the ultraviolet radiation as compared with P. bursaria.
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