302 METHODS OF STERILISATION. 



able to longest withstand influences adverse thereto. This group 

 alone has to be borne in mind in testing the efficacy and general 

 applicability of a method of sterilisation; since, if the same is 

 capable of destroying the organisms exhibiting the greatest power 

 of resistance, it will certainly, and much more quickly, deprive 

 all the remaining weaker ones of life. On the other hand, when 

 the contrary is not proved, it must always be assumed that the 

 object to be sterilised is infested with organisms of the highest 

 resisting power. 



These hardy organisms we are already acquainted with, namely, 

 the bacterial endospores, which in this respect have no equal, and 

 can therefore be made to serve as test objects for determining the 

 reliability of any germ-destroying process coining under examina- 

 tion. It has been already stated, in 53, that great differences 

 exist in the resisting powers of the spores of the various species of 

 bacteria ; but of course we have only to take the strongest into 

 consideration. According to the investigations hitherto made 

 these are : among the non- pathogenic varieties, those species 

 commonly known as the hay and potato bacilli; and among 

 the pathogenic bacteria, the anthrax bacilli. Bearing this in 

 mind, EGBERT KOCH (I.), the eminent medical bacteriologist, 

 employed as reagent for testing the efficacy of various disinfec- 

 tants spores of anthrax bacilli, which, for greater convenience 

 in application, he allowed to dry on silk threads. 



The articles of metal or glass to be sterilised are placed in a 

 case, formed on the plan of the drying-ovens used in chemical 

 laboratories, wherein they are heated to 150 C. for an hour. 

 During this time no diminution of temperature is permissible, 

 because if such a fall occurs, the labour will have been bestowed 

 in vain. KOCH and WOLFFHT)GEL (I.) have shown that there 

 are bacterial spores that are killed only after an exposure to air 

 at 140 C. for three hours. However, by an exposure to 150 for 

 one hour we may be sure that all the germs present have been 

 killed ; and air-filters fitted with cotton- wool (freed from fat) 

 are also sterilised by the same treatment, the cotton-wool assuming 

 thereby a yellowish to brownish coloration. Both the apertures 

 of such a filter must have been previously closed with plugs of 

 cotton, which must not be removed until the filter is about to be 

 used. It is necessary that glass articles should be dry before 

 they are introduced into the hot-air sterilising apparatus, since 

 otherwise they will crack. 



Small metal instruments, such as forceps and inoculating 

 needles, as well as the glass stoppers used for closing Pasteur 

 flasks, can be conveniently purified in the flame of a Bunsen 

 burner or spirit-lamp. 



