134 



Messrs. S. G. Shattock and L. S. Dudgeon. [Feb. 20, 



of the same medium and incubated with the rest. No growth ensued in the 

 case of any of the three heated slips ; the control gave a full growth of 

 B. pyocyaneus within 48 hours. 



January 13, 1912. — It being thus clear that the air-dried film of 

 B. pyocyaneus is killed by 15 minutes' heating at 100° C, a vacuum tube 

 containing a slip of this bacillus, which had been sealed off August 1, 1911, 

 after the usual treatment, was boiled for 45 minutes. 



The time selected was triple that of the minimum which had been found 

 lethal in the case of the air-dried film. The purpose of this was to ensure 

 that the film was raised to the temperature of 100° C, seeing that its heating 

 in vacuo would be delayed, owing to the absence of gas convection, and could 

 occur only by radiation, and conduction from the heated tube to the edges 

 of the glass slip in contact with its inner surface. After being boiled for 

 45 minutes, the tube was opened with the usual precautions, and the slip 

 transferred to litmus glucose broth, and incubated at 37° C. 



A second vacuum tube was then opened as a control, and the contained 

 slip transferred to another tube of the same medium ; the vacuum tube was 

 one of four which had been sealed off at the same time, viz., August 1, 

 1911 ; the slips in these four tubes had been inoculated from the same 

 peptone water culture of B. pyocyaneus. The slip from the boiled tube proved 

 to be sterile ; that from the control tube gave an abundant growth within 

 48 hours, which was identified by sub-culture as B. pyocyaneus. 



Proceeding with temperatures lower than 100° C, air-dried slips of 

 B. pyocyaneus (prepared as in all other cases, for the immediate occasion) were 

 treated in sealed tubes by submersion in water at 80° C, after having been 

 warmed for 15 minutes at the innocuous temperature of 40° C. One slip 

 was heated for 30 minutes, one for 60. Both proved to be sterile. The 

 air-dried, unheated, control slip, which was transferred to broth after the 

 completion of the heating of the others, gave a full growth. 



By the same method it was found that temperatures of 76° C. and of 65° C. 

 are lethal when maintained for an hour. 



The results show that in the case of B. pyocyaneus the lethal temperature 

 is practically the same, whether the micro-organism is subjected to it in the 

 wet state or the dry. 



We terminated these observations by heating a vacuum tube containing 

 a slip of B. pyocyaneus, sealed off August 1, 1911, for three hours at 65° C. in 

 a water bath. The film proved to be dead. The control, unheated, film in 

 another vacuum tube of the same batch (August 1, 1911). tested on the 

 same day, gave a typical and abundant growth within 48 hours. 



It appears plainly, therefore, from these observations that the resistance of 



