MEANS OF DISINFECTION 435 



sick rooms and hospitals, 2 per cent, carbolic, or 1-1000 solution of 

 mercuric chloride.* 



More recently a number of experiments have been carried out 

 in Europe and America as to the efficacy of certain chemical 

 substances, and reference will be made subsequently to some of the 

 results. Much of the evidence has been of a conflicting nature 

 which is due, as we have said, to varying conditions, strengths of 

 disinfectants, and resistance of organisms. 



Two or three years ago several workers at Leipzig f drew up 

 simple directions, the adoption of which would considerably assist 

 in securing a common standard for disinfectant research. They were 

 as follows: 



1. In all comparative observations it is imperative that molc- 

 cularly equivalent quantities of the reagents should be employed. 



2. The bacteria serving as test objects should have equal powers 

 of resistance. 



3. The number of bacteria used in comparative observation should 

 be approximately equal. 



4. The disinfecting solution should always be used at the same 

 temperature in comparative experiments. 



5. The bacteria should be brought into contact with the dis- 

 infectant with as little as possible of the nutrient material carried 

 over. (This obviously will depend upon the object of the research.) 



6. After having been exposed to the disinfectant for a fixed time, 

 they should be freed from it as far as possible. 



7. They should then be returned in equal numbers to the 

 respective culture medium most favourable to the development of 

 each, and kept at the same, preferably the optimum, temperature 

 for their growth. 



8. The number of surviving bacteria capable of giving rise to 

 colonies in solid media should be estimated after the lapse of equal 

 periods of time. J 



Means of Disinfection 



We may now mention shortly some of the commoner methods 

 and substances adopted to secure efficient disinfection. They are all 

 divisible, according to Buchanan's standard, into two groups : 



1. Heat in various forms ; 



2. Chemical bodies in various forms. 



In practical disinfection it is necessary to inhibit or kill micro- 

 organisms without injury to, or destruction of, the substance harbour- 



* Sternberg's Bacteriology, p. 201 et seq. 

 t Zeitschr. f. Hyg. und Inf. Krank. , xxv. 



See also " Standardisation of Disinfectants," by Rideal and Walker, Jour, of 

 Sanit. Inst., 1903. 



