174 ANTISEPTICS 



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. 

 Kronig and Paul introduced what is known as the Garnet method for 

 testing antiseptics. In this, small garnets of equal size are carefully 

 cleaned, dipped in an emulsion of anthrax spores, and allowed to dry. 

 They are then placed in mercuric chloride, and from time to time some 

 are removed, gently washed, and treated with ammonium sulphide to 

 decompose the chloride. They are then well shaken in a measured 

 quantity of water. This is plated, and the number of anthrax colonies 

 developing is counted. 



Ponder and Woodhead have introduced an ingenious apparatus by 

 which the effects of different concentrations of an antiseptic on the 

 vitality of such an organism as the b. coli can be automatically 

 recorded. 



Much attention has been paid to the standardisation of antiseptics. 

 and a watery solution of carbolic acid is now generally taken as the 

 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 2^ minutes to 15 minutes. Perform a 

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

 parative result in multiples 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. 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 considered 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 



