Survival and Reproduction of Paramecium after X-irradiation

Four species of Paramecium, P. calkinsi, P. mul-timicronucleatum, P. bursaria , and P. trichium , were treated in the following way. Counted numbers (100 or 200) were irradiated with X-rays in 2 ml air-tight Nylon syringes in steps of 50,000 r begining with this dosage and extending up to at least 450,000 r. For each experiment, the four different species were irradiated simultaneously each in one syringe. Survival and reproduction were then followed for at least 48 hours by expressing irradiated specimens from the syringes into spot plates. P. trichium was the most radiosensitive and recovery and reproduction occurred only after the lower dosages. P. calkinsi was the most radioresistant and showed relatively fast recovery and reproduction even after moderately high dosages. With certain high dosages, reproduction was blocked temporarily for 24-30 hours, after which there was not only recovery from irradiation but a gradually in creased reproductive rate. The greater the dosage, the slower the recovery to reproductive ability.