66 TEXT-BOOK OF BACTERIOLOGY. 



else from germs, it must be borne in mind that it may contain some 

 of the spores which it is so very difllcult to annihilate. In other 

 words, to effect sterilization, only such means must be employed 

 as experiment and experience have shown to be capable of regu- 

 larly and certainly killing even the most tenacious spores. 



This is no requirement based on theory and useless for every- 

 day practice. The incorrectness of such a view would soon be proved 

 by very unpleasant experiences. Bacilli and their spores exist, in 

 fact, everywhere, and the majority of failures made in working 

 with bacteria is traceable to the insuflBcient sterilization of the 

 substances and utensils employed. 



What means are at our disposal to attain the ends in view ? It 

 is not easy to arrive at a just appreciation of them, because for a 

 long time sterilization, in its proper sense, was not sufficientlj- dis- 

 tinguished from other similar procedures. A process was regarded 

 as fully sufllcient if it only checked the development of the bacteria, 

 and the fact was overlooked that as soon as the means was re- 

 moved its operation was at an end, and the checked bacterial 

 growth was resumed. We demand from a truly disinfecting mea- 

 sure that it should once for all destroy every trace of life in the 

 micro-organisms; that it should also infallibly annihilate their 

 most enduring forms. 



This requirement must, it is true, be taken "cum grano salis.'' 

 The different species of bacteria are by no means all alike as re- 

 gards the tenacious vitality of their spores. Some are known 

 which yield to slight attacks, and others that can only be destroyed 

 with the greatest difficulty. If the sterilizing process be applied to 

 these latter, requirements are met with which cannot be carried 

 out in practice. 



Fortunately, however, the varieties which it is so very difficult 

 to destroy are by no means frequent. It is sufficient to know 

 where to expect to meet with them; for instance, in garden mould, 

 in manure, and in decaying mixtures. In such cases it is, of course, 

 necessary to proceed with extra care. 



In ordinary cases, however, sterilization may be accomplished 

 with less trouble, and the principles which sterilization should fol- 

 low for purposes of culture have, as a rule, been determined by 

 careful investigations, and are as follows: 



It has been found that a small number of chemical agents are 

 capable of accomplishing what is required. Abo^'e all, as specially 

 important must be mentioned concentrated carbolic acid, corrosive 

 sublimate in solution of 1 to 1,000, and also quick-lime. 



But the use of these substances in connection with the breeding 



