40 GROWTH OF BACTERIA 



which consists chiefly of sulphur-dioxide gas, has been 

 employed for a long time for the disinfection of 

 rooms in which fever patients have been nursed. The 

 sulphites of calcium and sodium are also valuable 

 disinfectants, and much used in breweries for the 

 cleansing of foul casks and other utensils. 



The so-called i( chloride of lime " is frequently employed 

 as a disinfecting agent, its effectiveness in this respect 

 depending upon its power of giving off free chlorine 

 gas, which latter very rapidly destroys living bacteria 

 and their spores, especially when moisture is present. 



A 10 per cent, solution of carbolic acid or phenol 

 (C 6 H 5 OH) has disinfecting properties, but weaker 

 solutions do not effectively destroy the spores of bacteria. 



Formaldehyde (CH 2 O) during the last few years has 

 been utilized for the destruction of micro-organisms. It 

 is very active, solutions containing .1 to .2 per cent, of the 

 compound being sufficient to kill the spores of most 

 bacteria in less than an hour. 



In weak solutions all the above-mentioned sub- 

 stances are good antiseptic agents. To this list of 

 chemicals may be added thymol, toluene, chloroform, 

 salicylic acid, boric acid, borax, lime-wash, and alcohol, 

 all of which may be employed for retarding putrefaction 

 and other changes induced by bacteria. 



One-half to one per cent, of toluene (C 6 H 5 CH 3 ) is 

 frequently utilized to check the development of bacteria 

 in various solutions whose enzyme action it is desirable 

 to study. Chloroform (CHC1 3 ), thymol, and salicylic 

 acid (C 6 H 4 OH.CO 2 H) may be used for a similar 

 purpose. 



Freshly-burnt quicklime (CaO), when slaked and made 

 into a " whitewash," is a cheap and valuable disinfectant 



