1885.] 



Studies of Disinfectants by New Methods. 



259 



VI. "Studies of Disinfectants by New Methods." By 

 A. Wynter Blyth, Medical Officer of Health. Commu- 

 nicated by Dr. B. W. Richardson, F.R.S. Received 

 October 8, 1885. 



The object of tbis paper is to communicate the results of a study 

 of the action of disinfectant substances which has occupied the leisure 

 of the author for the past eighteen months. Three series of experi- 

 ments have been made, viz. : — 



1. On the Bacterium termo. 



2. On the various micro-organisms in sewage. 



3. On the disinfection of typhoid excreta. 



The term disinfectant as used throughout this paper must be con- 

 sidered as synonymous with " germicide " ; to disinfect a thread or a 

 drop of liquid contaminated by bacteria is, according to my view, to 

 kill, and to kill not by a destructive or corrosive, but by a true 

 poisonous action, all the micro-organisms, so that the " disinfected " 

 micro-organisms placed under the most favourable conditions for 

 growth are incapable of any further development. 



1. The Disinfection of the Bacterium termo. 



A pure cultivation of the Bacterium termo was made in ordinary 

 sterile, solid, nutrient gelatin; the somewhat fluorescent greenish 

 liquid to which the upper layers of the gelatin were reduced, by the 

 growth and multiplication of the bacterium, was submitted to the 

 various disinfectants in the manner to be described, and then the 

 bacterium was withdrawn as far as possible from the influence of the 

 disinfectant and planted, as it were, in fresh nutrient gelatin. The 

 methods used in the sterilisation of beakers, test-tubes, &c, as well as 

 the preparation of nutrient gelatin, differed in no essential respect 

 from the same methods in general use in biological laboratories, and 

 therefore need not be described. 



The B. termo was submitted to the action of the disinfectants by 

 two methods, which may be called the " drop " and " thread " method 

 respectively. 



The Drop Method. — Sterilised pure water was infected with a few 

 c.c. of gelatin liquefied by the bacterium ; measured volumes of this 

 infected water were added to measured volumes of the disinfectant, 

 and the whole allowed to act for twenty-four hours. A drop of this 

 liquid was then added to from 10 — 20 grams of the nutrient gelatin, 

 first liquefying it at a very gentle heat. As the proportion of the 

 weight of the drop to the weight of the nutrient gelatin varied from 

 about 1 : 500 to 1 : 1000, the dilution was in most cases sufficient to 



