STANDARDIZATION OF DISINFECTANTS 



145 



actions, and it is interesting therefore to ascertain whether it applies also to the 

 reaction of disinfection. The formula is : 



A=^^Mog5^ 



Tm ® "IT 



where Kq and K„ are the velocity constants of the reaction in question corre- 

 sponding to the absolute temperatures To and T„ respectively, and A is a con- 

 stant. As the time taken for the completion of a reaction may be considered 

 as inversely proportional to the velocity of the reaction, this equation may be 

 re-written thus : 



= —. log — 



where t^ and ^o are the times taken to complete the reaction ai absolute tem- 

 peratures T„ and To respectively. 



This formula was found by Madsen and Nyman to apply to the killing 

 of anthrax spores by HgClj. Chick showed that it was likewise applicable to the 

 disinfection of paratyphoid bacilli by HgClg, AgNOg and phenol (Table 19). 



TABLE 19 

 HgClz 1/10,000. Paratyphoid Bacilli. (Modified from Chick 1908.) 



For AgNOg the value of A was 5450, add for phenol 8430. 



Whether rise of temperature afiects the velocity of disinfection in a simple 

 logarithmic manner or in accordance with the law of Arrhenius, it is impossible 

 to say, for within a small range of temperature the two become almost identical 

 (Chick 1910). Belehradek (1926) brings evidence to suggest that Arrhenius' 

 formula is not generally applicable to the influence of temperature on biological 

 processes. 



It must be pointed out that when an organism is suspended in a favourable 

 medium, the effect of temperature on inhibition of growth may be the exact opposite 

 of that on disinfection. Thus Behring found that the growth of anthrax bacilli 

 at room temperature was inhibited in the presence of 1/400,000 HgClz ; at 37° C. 

 a concentration of 1/100,000 was necessary to inhibit growth. It appears that 

 the rise of temperattire favours the growth of the bacilli more than it does the 

 action of the germicide. Similar results were obtained by Chick (1908) with para- 

 typhoid bacilli and phenol. 



Standardization of Disinfectants. — In the practical application of disinfection, 

 it is desirable to have some measure of the relative germicidal activity of different 

 disinfectants. The first method devised for this purpose was Koch's (1881) thread 

 method. Suitable organisms, such as anthrax spores, were dried on silk threads, 

 submitted to the action of the disinfectant, and subsequently washed, and trans- 



