THE ACTION OF ANTISEPTICS. . 141 



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 anti- 

 septic 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 preferable 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 an albuminate 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 to the bacteria is swamped in an excess of culture fluid, can safely be 

 followed, especially when a series of antiseptics is being compared. 



The Action of Antiseptics. In inquiries into the actions of 

 antiseptics attention to a great variety of factors is necessary, 

 especially when the object is not to compare different antiseptics 

 with one another, but when the absolute value of any body is 

 being investigated. Thus the medium in which the bacteria to 

 be killed are situated is important; the more albuminous the 

 surroundings are, the greater degree of concentration is required. 

 Again, the higher the temperature at which the action is to take 

 place, the more dilute may the antiseptic be, or the shorter the 

 exposure necessary for a given effect to take place. The most 



