[SHANLY] HEAT RESISTANCE OF BACTERIAL SPORES 139 



at my disposal was inadequate. A subsequent paper will demon- 

 strate that I have, with Dr. Malone, endeavored to meet this ob- 

 jection. 



II. I fully recognize the cogency of Principal Harrison's second 

 criticism, and am quite prepared to find that there is a difference in 

 the heat resistance of spores according as to whether the strain has 

 been for many generations in the laboratory or has recently been isola- 

 ted. I have kept this matter in mind. It will be observed in the 

 table here given (page 14) that two strains of both B. Megatherium 

 and B. subtilis showed variation in resisting powers. I have isolated 

 two new strains of these forms and tested them soon after isolation. 

 Both withstood the relatively high temperature of 90 °C. for one hour. 

 It may therefore be found that the spores of forms growing naturally 

 possess higher resisting powers than those of forms growing for long 

 periods in the laboratory. If this be true, it will, however, only sup- 

 port further my main deduction, that heat resistance is a variable 

 quantity. 



III. As to a possible discrepancy between the results here re- 

 corded and those of previous observers, it may be pointed out that this 

 discrepancy is really only apparent. Previous observers have with 

 rare exceptions employed a much shorter period during which the 

 spores have been exposed to the given temperature. The results of 

 those observers who have most nearly approached our method of 

 testing spore resistance are, if they be analysed, similar results. For 

 example, Weil^ notes that he has only very occasionally come across 

 strains of Anthrax bacillus yielding highly resistant spores, and he and 

 DannappeP both point out that Anthrax spores are rapidly destroyed 

 by streaming steam. 



The former pointed out that rarely do the spores resist streaming 

 steam for one minute: the latter found that 70 percent of Anthrax 

 strains afforded spores which would not resist streaming steam for one 

 minute. With many cultures five to fifteen seconds exposure was suffi- 

 cient to destroy the spores, and Weil found no strain which would 

 stand this exposure for seven minutes. This is little in accord with the 

 general opinion regarding the extraordinary resisting powers of the 

 spores. Nor must we confuse results obtained by subjecting spores 

 to the influence of anhydrous solutions such as glycerine and oil. 

 As Bullock^ has shown. Anthrax and Subtilis spores require to be 

 heated to 170°C. for at least half an hour, or to 180°C. for ten minutes 

 when immersed in these fluids in order to kill them surely. In other 

 words they may as well be subjected to dry heat at the ordinary at- 



iCtbl. f. Bakt. Abt. I, 30, 1911, 50o! 



2 Ref. in Ctbl. f. Bakt. Abt. 4, 6, 1900, 841. 



