The Ferment-action of Bacteria. 



543 



Tubes of 10 per cent, gelatine were inoculated with the five 

 microbes, and placed in the incubator at 37° C, with the exception of 

 the putrefactive micrococcus, which was kept at 22° 0. 



When liquefaction was complete the fluid was filtered into sterile 

 tubes, the bacterial deposit being washed with a small quantity of 

 sterile distilled water. 



Of the filtrate, one, three, and five drops were added respectively 

 to fresh gelatine, and the tubes placed in the incubators as before. 

 The gelatine liquefied, and in all cases bacteria were present. 



This liquefied gelatine was in its turn taken and subjected to a 

 temperature of 50° C. for one hour. Then one, three, and five drops 

 were added to fresh gelatine. After incubating, some of the cholera 

 comma tubes did not liquefy, but in all cases where liquefaction took 

 place it was due to the active bacteria, as proved by their growth on 

 control plates. The control plates were made by adding a few 

 drops of the liquefied gelatine to fresh gelatine, and pouring it out in 

 a sterile glass dish. After incubating at 22° C, the gelatine was 

 examined microscopically, and the presence or absence of bacterial 

 colonies noted. 



The liquefied gelatine was next subjected to a temperature of 

 100° C. for fifteen minutes. The same number of drops were added 

 to gelatine. This fresh gelatine did not liquefy. Finally, c.c. were 

 added to fresh gelatine, but still it did not liquefy. 



The control plates showed no colonies. 



We therefore conclude that exposure to a temperature of (I) 

 100° C. destroys— 



(a.) The bacteria. 



(b.) The liquefying power of the fluid. 



(II) 50° C. does neither. It was not deemed advisable to continue 

 the sterilisation too long, having regard to the injurious action of heat 

 on soluble ferments. 



It was next necessary to determine the temperatures between 50° C. 

 and 100° C, which would be sufficient to kill the bacteria without 

 rendering any ferment which might exist inactive. A series of 

 experiments led to the following results : — 



60° C. for half an hour killed Koch's and Finkler's spirillum. 



75° C. for fifteen minutes, on two successive days, killed the scurf 



and " Welford " bacilli. 

 70° C. for fifteen minutes, on two successive days, destroyed the 



putrefactive micrococcus. 



Having established these facts, a series of cultures at 37° C. were 

 made in small glass flasks, each containing about 100 c.c. of 10 per 

 cent, gelatine. The liquefied gelatine was filtered, and the deposit 

 washed with sterile distilled water. 



vol. xlvi. 2 



