276 



Studies of Disinfectants by New Methods. [Nov. 26, 



upon, the number of colonies per gram of typhoid developed in a 

 normal solution acting for twenty-four hours was as follows : — 



No. of colonies per gram 

 of typhoid matter 

 taken. 



Parvoline, C 9 H 13 N 5,882 



Pyridine, C 5 H 6 lSr 6,000 



Picoline, C 6 H 7 N" 16,949 



Lutidine, C 7 H 9 N 19,355 



Summary. — From the three series of experiments certain general 

 conclusions may be drawn ; these are as follows : — 



1. The relative merits of phenol and cresol as a disinfectant are 

 fairly equal, as shown by experiments on Bacterium termo and on 

 sewage, so that preference for one or the other must be determined 

 from considerations apart from degrees of activity.* 



2. Ferrous sulphate as a disinfectant of Bacterium termo, of sewage, 

 and of typhoid excreta is shown to be unreliable. Even strong 

 solutions fail to destroy all classes of micro-organisms. Considering 

 the extensive use of ferrous sulphate in cases of typhoid fever, and 

 that in both scientific and popular manuals ferrous sulphate is 

 confidently recommended as a disinfectant of specific excreta, it seems 

 important to accentuate the fact that my experiments are in their 

 result wholly opposed to the popular view and custom. 



3. The experiments on the amines clearly show that the disin- 

 fectant action of members of that series differs in degree according to 

 the displacement of hydrogen by methyl, ethyl, propyl, or hydroxyl. 

 The connexion between chemical constitution and disinfectant 

 action is also seen in the experiments on the pyridine series, but is not 

 so marked. 



4. Other things being equal, the shorter the time a disinfectant 

 acts, the less the disinfection ; this was shown very clearly in the 

 experiments on typhoid excreta treated with cresol for varying 

 periods of time. It, therefore, necessarily follows that even when 

 strong disinfectants are poured on to specific excreta, and the whole 

 within a few minutes thrown into a drain or cesspool, which by 

 great • dilution more or less removes the excreta from the sphere of 

 disinfectant influence, no true disinfection has been accomplished. 



5. Disinfection is far more efficient at 35 - 5° to 37°, the temperatures 

 at which development and growth of micro-organisms is most active, 

 than at ordinary temperatures. This is shown in the experiments on 

 Bacterium termo with phenol, cresol, lutidine, collidine, and potassic 

 permanganate, as well as in the experiments in the treatment of 

 sewage with chloride of lime and potassic permanganate. 



* See foot-note on p. 268. 



