102 



KowiiUh: (1) CheclcH. I'.olli lulxs clinnlcd inside of 4S liniirs and 'Icveloped 

 iiuniially. (2) Coolcrl i|iii<kly. Butli tul)cs rcmairKMl })erl'ectly clear till the end of 

 the experiment (.33 davH). (3) (V)olc(l sluwly. Both tubes remained clear until the 

 ninth day. Then one i)f them l)eciime very feehly clomled and jiradnally pasned 

 throuKli the same chan^ieH as the check fnhes, hut never caught up with tin' latter. 

 Tlic (itlicr tulic cnntiinicil clear till the cikI of the ex prrinicnt. 



As !i result, <tl' tlicsc cxpcriiiicnts we may conclude that exposure of 

 7V hyactntJii for in luiiuites to a temperature of 43*^ C. does not 

 apprecia])ly retard j^rowth; \\ retards u-rowth slinlitly; 45'^ retards 

 considera])ly; 40' to 4(5.50 destroys the oreater part of the or<ran- 

 isms; 47.17 to 47.45' (mostly 47.20 to 47.80 ) desti-oys ahiiost all; 

 47. ns to 47.SO' (mostly 47.r>0 to 47.70' ) destroys all. 



The thermal death point, therefore, under the exact conditions 

 named, may l)e recorded as ai)proximat«dy 47.60' , Imt a majority of 

 the rods are killed at 46.50° C. 



Pro})al)ly some of the rods are destnn'ed hy lo minutes' exposure 

 to temperatures as low as 45 ' or 45.50°. Exposures lor nuu-h longer 

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

 liave the same effect, as may be seen from what follows. 



Tlu^ thermal death ])oint of Px. Kf(^mrt/ in +15 ))eef l)ouillon is 

 ai)proximately 53° C. In Uschinsky's solution it is a little higher. 



The thermal death point of Z^-. phaxeoJl is approximately 4H.50°, 

 and that of 1\. campcKiriK^ is 51-50 . 



Maximcm 'i'i;Mi>i;nA riKic i-oit < titowTii. 



The maxiimun temi)erature at which V's. Injucivtlti will grow in 

 favora))h! media is 34' to 35° C, the exact temperature limit varying 

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

 individual rotls. This conclusion rests on the following experiments, 

 which were made in a R()hr])cck thermostat, covered with thick hair- 

 cloth and provided with a lai'ge water reservoir, so that the culture 

 chamber is not ([uickly sensitive to changes in gas ])ressure or in the 

 temperature of the room. 



(1) In stock 244c (0 jielatin), kej)t in the thermostat at 40° C, there was no 

 •jfrowth whatever, and noni' ai)peare(l when this tube was removed from the thermo- 

 stat at the end of 7 days and kept at room tem])eratnres for an additional 3S days. 

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

 had been cloudy for (i days. In a second tube of this gelatin, in(tculated 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 |)()tato cylinders (stock 24(>) were inoculated at the same time and from 

 the same culture as the 2 tubes of gelatin. One of the.se was i)ut into the thermostat 

 at 40° C. and the other 2 were kept at room temi)eratures. 



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 



