26 STERILIZATION BY ANTISEPTICS 



SECTION IV. STERILIZATION BY ANTISEPTICS. 



Sterilization by antiseptics has but limited use in bacteriological work. 

 The addition of antiseptics will it is true destroy micro-organisms in a 

 medium designed for the growth of cultures, but the amount of antiseptic 

 which has to be added to effect this result is very much greater than 

 the amount required to inhibit the multiplication of any organisms 

 which may subsequently be sown in it ; the medium is therefore rendered 

 useless. 



1. Antiseptics are, however, in general use for sterilizing the interior of 

 glass dishes, bell jars, and other similar articles which are to be used to 

 protect from dust and contamination Petri dishes, culture tubes, etc., and 

 which will not come in contact with any culture medium, or with the organisms 

 under investigation. Fixed non-volatile antiseptics must be employed 

 since the vapours given off by volatile compounds hinder the growth of 

 organisms on culture media. 



A 0*1 per cent, solution of perchloride of mercury may be used. The 

 solution should be made with distilled water, but if tap water be used a 

 small amount (O5-1 gram) of tartaric, acetic or hydrochloric acid must 

 be added to prevent precipitation of the mercury salt by the salts dissolved 

 in the water. 



Perchloride of mercury has however now been almost entirely discarded 

 in favour of oxycyanide of mercury in Ol per cent, solution. This solution 

 though powerfully antiseptic has no caustic action, it does not precipitate 

 albuminoid substances, neither does it attack instruments and other metal 

 articles. 



2. Antiseptics are also in general use for sterilizing the hands, and for 

 washing out vessels and sterilizing instruments during inoculation and 

 other experiments. Solutions of Ol per cent, of perchloride or oxy- 

 cyanide of mercury or 1*5 per cent, of formalin are often used for these 

 purposes. 



[Lysol, a solution of the three cresols in soap and water, is a particularly 

 useful antiseptic. In 2 per cent, solution it does not hurt the skin, and the 

 soap in solution makes a lather if the hands be washed in it or if the surface 

 of the skin be rubbed with a sponge soaked in the solution ; the presence 

 of the soap makes a solution of lysol a more efficient antiseptic for these 

 purposes than mercury solutions. Lysol does not damage metal instruments, 

 and does not precipitate albuminoid solutions. If made up in large quan- 

 tities with hard water the soap is liable to be precipitated to some extent, 

 but the antiseptic constituents still remain in solution.] 



Solutions of perchloride or oxycyanide of mercury may also be used for 

 sterilizing the surface of the skin before collecting pus, blood, etc., from the 

 living subject (Chap. XII.). Care must of course be taken that, after steriliza- 

 tion, all traces of the antiseptic are removed by washing the part well with 

 alcohol before collecting the material, otherwise the presence of the anti- 

 septic would materially interfere with the subsequent growth of organisms 

 in culture. [At the present time, however, it is more usual to paint the sur- 

 face of the skin with tincture of iodine (British Pharmacopoeia) before 

 penetrating it for the purpose of collecting material for bacteriological 

 investigation.] 



3. Antiseptics are also added to sterile filtrates which are no longer 

 required as culture media. For this purpose a small quantity of some 

 antiseptic (such as thymol or camphor) which is without chemical action 

 on the constituents of the fluid is selected. 



