BY R. GREIG-SMITH. 



847 



cells were not dead but were encysting. The older cells at iV 

 or 42° moved about, but, at 43°, they had come to rest, and a 

 few showed the cilia moving slowly, while others were rounded 

 and entire or had apparently burst. At 44°, they were spherical 

 or slightly ovoid, and were apparently encysting. 



The amoebae began to be affected at 43°, when their motility 

 ceased. At 44°, they were rounded or spherical, some with the 

 pulsating vacuole active, others with it still. That they were 

 not dead, was shown by their refusing to take up methylene 

 blue. 



The flagellates became non-motile and irregularly shaped at 

 39°, and did not take the stain. Tabulating these observations, 

 we have : — 



Omitting the flagellates, which appear irregular, the action of 

 heat upon the protozoa is very similar to the action of the volatile 

 disinfectants. Paramaecium is quickly destroyed, while the 

 amoebae are less affected than Colpoda. Still, there should be a 

 greater difference between the amoebae and the mature colpodae. 



The motile colpodae and amoebae, after becoming immobilised 

 and rounded at 44° and 45°, behaved to stains as if they were 

 still alive and encysting, but they really had become so altered 

 that subsequent growth in nutrient solutions did not occur. 

 This was shown by suspensions, which contained motile forms 

 only, becoming sterilised after being heated for ten minutes at 

 45° (amoebae), and 46° (colpodae). 



The lethal temperature of the protozoa, as occurring in the 

 soil, is always higher than the motile forms, on account of the 

 presence of cysts. Work upon such encysted forms has been 

 done by others, but a few tests are given, chiefly to show the 

 influence of the culture-fluid. 



