Thermal Death-point of Monad Germs. By W. II. Ballinger. 13 



up to 300° Fahr., kept at that heat for ten minutes, and then 

 allowed slowly to cool. 



When cool, the specially prepared cell was at once carefully 

 examined with an immersion lens giving 2000 diameters. Nothing 

 could be seen but violent Brownian movement. The same was true 

 in every respect of the other five cells, which were continuously 

 examined by rotation. The five control cells were kept under 

 examination for eight days, and the cell in which the spores 

 had been inserted for fourteen days, but no trace of the monad 

 appeared, and, in fact, they are sterile to this day. 



The fluid in these cells was manifestly devitalized, or rather 

 the action of the heat upon the spores had been destructive. I 

 next repeated the whole experiment as before, but at a temperature 

 of 275° Fahr. The results were precisely similar, there was no 

 subsequent appearance of the Hving monad in any stage. 



The next experiment was made at 265° Fahr., one cell being 

 germ-inoculated, and five not so, as before. 



On examination everything was as in the former instances, 

 and continued so for two hours and a half. The cells had been 

 examined in rotation as before, special attention being given to the 

 real experimental cell. At the end of this time I became convinced 

 that I could see on the floor of one part of the cell, what I had not 

 been able to see in earlier examinations ; and I had a strong 

 suspicion of the same phenomenon in one other of the cells. I of 

 course confined myself to the one specially prepared ; and in the 

 course of an hour there was no doubt whatever that the monad 

 whose spore had been inserted, was in the cell in a developing con- 

 dition. In Fig. 14 (Plate II.) I give a drawing with camera lucida 

 of the field forty-five minutes after my detection of the new feature. 

 It will be seen by comparison of the groups a, a with the illustra- 

 tions given of the developmental history of this form,* that these 

 are stages in that development, and they were, in this instance, 

 steadily followed into the adult stage, and into the remarkable 

 condition of multiple fission characteristic of this monad. 



By a series of further experiments, with temperatures ranging 

 between 265^ and 270'' Fahr., the conclusion was reached, that this 

 organism, so far as our experience had gone the most successful in 

 heat-resistance of all the monads, had its spore destroyed at 

 a temperature of from 267° to 268^ Fahr. when the heat was 

 sustained in its normal fluid. 



Each of the other five forms was subjected by means of its spores 

 to precisely the same test ; and with the following results, viz. : — 



One (the "Calycine" portrayed in Fig. 12) had its spore de- 

 vitalized in fluid at the normal boiling-point of water, 212^ Fahr. 



In a dry heat it could endure 250^ Fahr. 



* 'Mon. Micr. Journ.,' xi. p. GO, &c. 



