142 ANTISEPTICS 



and the bodies having such a capacity are called antiseptics. It 

 is now known that the activity of these agents is limited to 

 the killing of bacteria outside the animal body, but still even 

 this is of high importance. 



Methods. These vary very much. In early inquiries a great point 

 was made of the prevention of putrefaction, and work was done in the 

 way of finding how much of an agent must be added to a given solution 

 such as beef extract, urine, etc., in order that the bacteria accidentally 

 present might not develop ; but as bacteria vary in their powers of re- 

 sistance, the method was unsatisfactory, and now an antiseptic is usually 

 judged of by its effects on pure cultures of definite pathogenic microbes, 

 and in the case of a sporing bacterium the effect on both the vegetative 

 and spore forms is investigated. The organisms most used are the 

 staphylococcus pyogenes, streptococcus pyogenes, and the organisms of 

 typhoid, cholera, diphtheria, and anthrax the latter being most used 

 for testing the action on spores. The best method to employ is to take 

 sloped agar cultures of the test organism, scrape off the growth, and mix 

 it up with a small amount of distilled water and filter this emulsion 

 through a plug of sterile glass wool held in a small sterile glass funnel, 

 add a measured quantity of this fluid to a given quantity of a solution 

 of the antiseptic in distilled water, then after the lapse of the period of 

 observation to remove one or two loopfuls of the mixture and place them 

 in a great excess of culture medium. Here it is preferable to use fluid 

 agar, which is then plated and incubated ; such a procedure is prefer- 

 able to the use of bouillon tubes, as any colonies developing can easily 

 be recognised as belonging to the species of bacterium used. In dealing 

 with strong solutions of chemical agents it is necessary to be sure that 

 the culture fluid is in great excess, so that the small amount of the 

 antiseptic which is transferred with the bacteria may be diluted far 

 beyond the strength at which it still can have any noxious influence. 

 Sometimes it is possible at the end of the period of observation to 

 change the antiseptic into inert bodies by the addition of some other 

 substance and then test the condition of the bacteria, and if the inert 

 substances are fluid there is no objection to this proceeding, but if in 

 the process a precipitate results, then it is better not to have recourse 

 to such a method, as sometimes the bacteria are carried down with the 

 precipitate and may escape the culture test. The advisability of, when 

 possible, thus chemically changing the antiseptic was first brought to 

 notice by the criticism of Koch's statements as to the efficacy of 

 mercuric chloride in killing the spores of the b. anthracis. The method 

 he employed in his experiments was to soak silk threads in an emulsion 

 of anthrax spores and dry them. These were then subjected to the 

 action of the antiseptic, well washed in water, and laid on the surface of 

 agar. It was found, however, that with threads exposed to a far higher 

 concentration of the corrosive sublimate than Koch had stated was 

 sufficient to prevent growth, if the salt were broken up by the action of 

 ammonium sulphide and this washed off', growth of anthrax still occurred 

 when the threads were laid on agar. The explanation given was that 

 the antiseptic had formed analbuminate with the case of each spore, and 

 that this prevented the antiseptic from acting upon the contained 

 protoplasm. Such an occurrence only takes place with spores, and the 

 method given above, in which the small amount of antiseptic adhering 



