778 A MANUAL OF BACTERIOLOGY 



carbolic-acid coefficient of many disinfectants (see pp. 760, 767, 

 and table, p. 770). Among the substances suggested are urine, 

 faeces, 2 per cent, suspension of dried and sterilised fasces (Martin 

 and Chick), rice starch, and milk. Kenwood and Hewlett found that 

 the presence of urine or faeces reduced the carbolic acid coefficient 

 of some proprietary disinfectants to a greater relative extent 

 than that of carbolic. 



The method is also sometimes somewhat erratic in practice, 

 and a number of determinations may be needed before the 

 strengths of disinfectant and carbolic which coincide are found. 

 Occasionally also two strains of E. typhosus may differ widely as 

 regards the germicidal action of the disinfectant on them, while 

 they are practically identical as regards the germicidal action 

 of the carbolic. 



The Kideal- Walker method is particularly applicable to the 

 coal-tar disinfectants which act rapidly and are used for sanitary 

 disinfection. It is unsuitable for the determination of the germi- 

 cidal value of the more slowly acting disinfectants. The con- 

 ditions of the test also render it unsuitable for the determination 

 of the germicidal value of disinfectants which are to be used in 

 the treatment of wounds where there is much organic matter 

 and the temperature approximates to 37 C. For the latter 

 Emery's method may be applied (No. 6 below). 



Woodhead and Ponder proposed a modification of the method. 

 In this, B. coli is used as the test-organism and bile-salt peptone 

 water as the culture medium, a platinum spoon being used for 

 culturing, and more cultures at shorter intervals up to half an 

 hour are made. 



(4) Volatile disinfectants may be tested by moistening the 

 wool plug of an agar tube, inoculating the agar, and capping 

 with a rubber cap, and observing whether any growth occurs. 



(5) Volatile disinfectants may also be tested by exposing 

 silk threads, pieces of paper or fabrics, splinters of wood, etc., 

 impregnated with organisms, some free, others done up in packets 

 of cotton-wool, in a room or chamber of known cubic capacity, 

 to the action of the gas. a known amount of which is present in 

 the chamber. After exposure for a given time, the threads are 

 sown in broth or agar tubes, and the tubes incubated. 



(6) Emery's method. " Ke-constituted " blood is prepared as 

 follows : Some blood is collected aseptically, allowed to coagulate, 



