102 



Results: (1) Checks. Both tubes clouded inside of 48 hours and developed 

 normally. (2) Cooled quickly. Both tubes remained perfectly clear till the end of 

 the experiment (33 days). (3) Cooled slowly. Both tubes remained clear until the 

 ninth day. Then one of them became very feebly clouded and gradually passed 

 through the same changes as the check tubes, but never caught up with the latter. 

 The other tube continued clear till the end of the experiment. 



As a result of these experiments we may conclude that exposure of 

 Ps. hyacinthi for 10 minutes to a temperature of 43*^ C. does not 

 appreciably retard growth; 14"^ retards growth slightly; 45^ retards 

 considerabl}-; 46^ to 46.50° destroys the greater part of the organ- 

 isms; 47.17° to 47.45° (mostly 47.20° to 47.30°) destro3^s almost all; 

 47.58° to 47.80° (mostly 47.60° to 47.70°) destroys all. 



The thermal death point, therefore, under the exact conditions 

 named, may be recorded as approximately 47.50°, but a majority of 

 the rods are killed at 46.50° C. 



Probably some of the rods are destroyed by 10 minutes' exposure 

 to temperatures as low as 45° or 45.50°. Exposures for much longer 

 periods to temperatures a few degrees lower, e. g., 7 days at 40° C, 

 have the same effect, as ma}^ be seen from what follows. 



The thermal death point of Ps. siewarti in +15 beef bouillon is 

 approximately 53° C. In Uschinsky's solution it is a little higher. 



The thermal death point of Ps. 2^^ciseoU is approximate h^ 49.50°, 

 and that of Ps. campestris^ is 51.50°. 



Maximum Temperature foii Growth. 



The maximum temperature at which Ps. Kyctcinthi will grow in 

 favorable media is 34° to 35° C, the exact temperature limit varying 

 somewhat with the medium used and with the heat resistant power of 

 individual rods. This conclusion rests on the following experiments, 

 which were made in a Rohrbeck thermostat, covered with thick hair- 

 cloth and provided with a large water reservoir, so that the culture 

 chamber is not quickly sensitive to changes in gas pressure or in the 

 temperature of the room. 



(1) In stock 244c (0 gelatin), kept in the thermostat at 40° C, there was no 

 growth whatever, and none appeared when this tube was removed from the thermo- 

 stat at the end of 7 days and kept at room temperatures for an additional 38 days. 

 This tube was inoculated with a very large loop from a beef-broth culture, which 

 had been cloudy for 6 days. In a second tube of this gelatin, inoculated from the 

 same culture at the same time and in the same manner, but kept throughout at 

 room temperatures of 24° to 34° C. (mostly 25° to 29°), the organism developed 

 normally, clouding the fluid in 24 hours. 



(2) Three potato cylinders (stock 246) were inoculated at the same time and from 

 the same culture as the 2 tubes of gelatin. One of these was put into the thermostat 

 at 40° C. and the other 2 were kept at room temperatures. 



Result: In each of the 2 check tubes the organism developed normally, the first 

 distinct sign of yellow growth being visible in about 47 hours. No trace of growth 

 appeared in the tube which was put into the thermostat, although a very large loop of 



