168 ANTISEPTICS 



standard with which other antiseptics are compared. Rideal and 

 Walker point out that 110 parts by weight of B.P. carbolic acid equal 

 100 parts by weight of phenol, and they recommend the following method 

 of standardising : To 5 c.c. of a particular dilution of the disinfectant 

 add 5 drops of a 24-hour-old bouillon culture of the organism (usually 

 b. typhosus), which has been incubated at 37° C. Shake the mixture 

 and make subcultures every 2J minutes to 15 minutes. Perform a 

 parallel series of experiments with carbolic acid, and express the com- 

 parative result in terms of the carbolic acid doing the same work. 



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 it 

 is, the greater degree of concentration is required, and this is the 

 reason why the action of antiseptics on bacteria in wounds is 

 limited in degree. 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 important factor, however, to be con- 

 sidered is the chemical nature of the substances employed. 

 Chick has shown that the action of a disinfectant upon a 

 bacterium presents close analogies with the interaction of simple 

 chemical substances, such as an acid and an alkali. In the case 

 of anthrax spores, during the first few minutes a great fatality 

 occurs, after which the action of the antiseptic gradually tails 

 off. With certain other organisms, however, such as the para- 

 typhoid bacillus, the presence in a culture — especially in a young 

 culture — of highly resistant forms renders the initial action of an 

 antiseptic less marked. Chick and C. J. Martin have further 

 investigated the effect of the presence of albuminous material in 

 a mixture of disinfectant and bacteria in decreasing the action 

 of the disinfectant, and consider that the latter is adsorbed by 

 the albumin. They believe that a disinfectant in an emulsion- 

 ised form is more efficient than a similar disinfectant in actual 

 solution, because of a similar phenomenon occurring ; for, 

 just as a disinfectant may be put out of action by being 

 adsorbed by organic particles, so when these organic particles 

 happen to be bacteria, the adsorption process cause* a greater 

 concentration of the antiseptic round the bacterial protoplasm, 

 and thus hastens its death. 



Though nearly every substance which is not a food to the 

 animal or vegetable body is more or less harmful to bacterial 

 life, yet certain bodies have a more marked action than others. 



