-I -CEPTIBILITY OF CELLS TO RADIUM RADIATION-. 167 



only Paramcecia from a pure culture, for unrelated wild cells show 

 great variations in their susceptibility to the rays. Another 

 necessary condition has been mentioned by Jacobs (4), namely, 

 that in each test the same amount of liquid must be used. 



THE REACTION OF PARAMCECIUM TO RADIUM RADIATION - 



When a Paramceciiim is exposed to radium radiations under the 

 conditions described, it quickens its movements at first and then 

 gradually slows down and ceases to swim unless thedi-h is -hakeii. 

 Later the contractile vacuoles pulsate more and more -lowly ami 

 finally stop, usually in the expanded condition. If radiation i- 

 longer continued, a typical cytolysis ensues. The cells imbibe 

 water, swelling considerably in consequence, and the ectopla-m 

 bulges out in the form of clear vesicles which later run together. 

 Then the pellicle separates from the rest of the cell carrying with 

 it the cilia. The protoplasm is now highly fluid. At thi- time 

 the macronucleus, in stained preparations, is seen to be divided 

 into several parts. Not infrequently the cells burst violently. 

 These phenomena are in every point similar to those which are 

 observed when Parania'cium is treated with a variety of cytolyiic 

 agents, as described by Biulgett (5), Harvey (6), and Jacobs 



THE RELATION OF TEMPERATURE TO SUSCEPTIBILITY. 



Rhodenburg and Prime (7) first pointed out that there is a defi- 

 nite correlation between temperature and the susceptibility of 

 cells when treated with X-rays. In their experiment- tlic\ 

 posed mouse sarcoma in vitro at a temperature of 42 (". 

 definite dose of X-rays, and then inoculated healthy mice \\ ith tin- 

 radiated cells. At this temperature 10 per cent, of the inocula- 

 tions failed to take. When the cells were radiated at 4.V ('.. 76 

 percent, of the inoculations failed. Control experiment- pn.\ed 

 that the-e temperatures alone are not sufficient to produce thi- 

 eiiect. The combination of high but sublethal temperature- 

 \\ith radiation was five times as effective as radiation alone. 



Mammalian tissue cannot be subjected to wide variation- in 

 temperature, but the Protozoa can live normally at temperature- 

 as low as 15 C. and as high as 37 C. In the following experi- 

 ment- these were the limits employed. 



When Paranicecia are radiated at hi-Ji temperatures, they sue- 



