332 SENSITIZATION TO HEAT 



sure coagulation occurs at 0°C. Gelatin, on the other hand, when 

 heat-sensitized by radiation liquefies at a lower temperature than 

 non-radiated gelatin.^ 



The method of experimentation was as follows: By means of a 

 method previously described^ a single organism from a pedigreed 

 culture of Paramecium caiidatum was exposed in a small drop of tap 

 water (always of the same size) to the rays emitted through the 

 fluorite window of a hydrogen discharge tube. The drop of water 

 containing the organism was maintained, unless otherwise stated, 

 both before and during the radiation at a temperature of 16-17°C. 

 After the exposure the organism was placed in a larger drop of tap 

 water in the concavity of a microscope slide on the warm plate of an 

 electric stove. The variable junction of a thermocouple (made with 

 No. 30 B. and S. gauge copper and "ideal" wires) was placed in the 

 drop with the organism. The thermocouple circuit contained a gal- 

 vanometer from which deflections corresponding to 0.1°C. could be 

 read. The temperatures of the dish from which the drop of tap 

 water was taken and the warm plate of the electric stove were so 

 controlled that no change of temperature, capable of being detected 

 by the galvanometer, occurred in the drop containing the organism 

 during the experiment. 



No attempt was made to heat all the organisms used in any one 

 experiment to precisely the same temperature. It was sufficient for 

 these experiments to keep the temperature within a certain range. 

 The organisms were exposed to the temperatures indicated below for 

 a period of 60 ± 3 seconds and were then transferred to a culture 

 drop and placed in the damp chamber with the controls for future 

 observation. The experimental results are given below. 



Control Experiments. 



Experiment 1. Effect of Radiation Alone. — Organisms were radi- 

 ated at 17-18°C., for 4 seconds and then transferred immediately 

 to culture drops without being placed on a temperature slide. 



^ Unpublished experiments by the writer. 



^ Bovie, W. T., and Hughes, D. M., Rate of recovery from the action of fluorite 

 rays, /. Gen. Physiol, 1918-19, i, 323. 



