CHEMICAL REAGENTS 27 



FILTRATION. 



1 . Cotton-wool filters (for the sterilisation of air and 

 gases) . 



2. Porcelain filters (for the sterilisation of various 

 liquids) . 



METHODS OF APPLICATION. 



Chemical Reagents, such as belong to the class known 

 as antiseptics (i. e., substances which inhibit the growth 

 of, but do not destroy, bacterial life), are obviously 

 useless. Disinfectants or germicides (i. e., substances 

 which destroy bacterial life) , on the other hand, are of 

 value in the disinfection of morbid material, and also 

 of various pieces of apparatus, such as pipettes, pend- 

 ing their cleansing and complete sterilisation by other 

 processes. To this class (in order of general utility) 

 belong : 



Lysol, 2 per cent, solution; 



Perchloride of mercury, o.i per cent, solution; 



Carbolic acid, 5 per cent, solution ; 



Absolute alcohol; 



Ether; 



Chloroform ; 



Camphor; 



Thymol; 



Toluol; 



Volatile oils, such as oil of mustard, oil of garlic. 

 Formaldehyde is a powerful germicide, but its pene- 

 trating vapor restricts its use. These disinfectants are 

 but little used in the final sterilisation of apparatus, 

 chiefly on account of the difficulty of effecting their 

 complete removal, for the presence of even traces of 

 these chemicals is sufficient to so inhibit or alter the 

 growth of bacteria as to vitiate subsequent experi- 

 ments conducted by the aid of apparatus sterilised in 

 this manner. 



