METHODS OF TESTING DISINFECTANTS. 467 



ant to the medium with which we are to determine if 

 the bacteria that have been exposed to its action have 

 been killed or not. 



The precautions that have hitherto been taken for 

 preventing this accident are, where the threads are em- 

 ployed, washing in sterilized distilled water and then 

 in alcohol ; or, where the fluid cultures were mixed with 

 the disinfectant in solution, an effort was usually made 

 to dilute the amount of disinfectant carried over to a 

 point at which it loses its inhibiting power. 



While these are sufficient in many cases, they do not 

 answer for all. Certain chemicals have the property 

 of combining so firmly with the threads upon which the 

 bacteria are located as to require other special means 

 of ridding the threads of them ; and in solutions in 

 which proteid substances are present along with the 

 bacteria a similar union between them and the disin- 

 fectant may likewise take place. In both instances this 

 amount of disinfectant adhering to the silk threads or in 

 combination with the proteid s must be gotten rid of, 

 otherwise the results of the test may be fallacious. A 

 partial solution of the problem comes from studies that 

 have been made upon corrosive sublimate in its various 

 applications for disinfecting purposes, and in this con- 

 nection it has been shown by Shaefer 1 that it is impos- 

 sible to rid silk threads of the corrosive sublimate 

 adhering to them by simple washing, as the sublimate 

 acts as a mordant and forms a firm union with the 

 tissues of the threads. Braatz 2 found the same to hold 

 good for catgut. For example, he found that catgut 

 which had been immersed in solutions of sublimate gave 



i Shaefer : Berliner klin. Woch., 1890, No. 3, p. 50. 



Braatz : Centr. f. Bakt. und Parasitenkunde, Bd. viii. No. 1, p. 8. 



