METHODS OF TESTING DISINFECTANTS. 515 



one, precautions must be taken against admitting this 

 minute trace of disinfectant to the medium with which 

 we are to determine if the bacteria that have been 

 exposed to the disinfectant have been killed or not. 



The precautions that have hitherto been taken to 

 prevent this accident are, where the threads are em- 

 ployed, washing them in sterilized distilled water and 

 then in alcohol; or, where 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 such precautions 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 proteids 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 ad- 

 hering to them by simple washing, as the sublimate 

 acts as a mordant and forms a firm union with the tis- 

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

 good for catgut. For example, he found that catgut 



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



2 Braatz ; Centr. f. Bakt. uud Parasitenkunde, Bd. viii. No. 1, p. 8. 



