A manual of bacteriology / by Herbert U. Williams.

Date:
1901
Catalogue details

Licence: In copyright

Credit: A manual of bacteriology / by Herbert U. Williams. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    176/304 (page 166)
    Determination of the disinfectant power of a substance is a problem of much greater magnitude, and the method used must be altered more or less to suit the properties of the substance tested. It is obvious that some of the sub- stance tested remains in contact with the organisms in the method given for determining the antiseptic value, and that we do not know whether the bacteria are alive and merely inhibited in growth, or actually killed. Sternberg's Method.—To a measured quantity of a virulent bouillon-culture of the test-organism is added a known quantity of the substance to be tested. After vary- ing lengths of time inoculations are made from this mi.xture into culture-media, preferably bouillon, and growth watched for under suitable conditions as to temperature and the like. The shortest exposure of the test-organism to the smallest quantity of the substance is taken as the germicidal value of that substance for the particular organism used. Koch's Method.—Usually employed for spore-bearing bacteria like the bacillus of anthrax. The hay bacillus is convenient to use when experiments are being made by large classes of students. Small pieces of sterile silk or cotton thread are soaked for some hours in a bouillon-cul- ture of the test-organisms. They are removed, partially dried, and then placed in a solution of known strength of the substance being tested, and exposed for a definite length of time. The thread is removed from the solution, washed carefully in sterile water, planted in bouillon, and growth is watched for. As in other methods, the greatest dilution of the germicide that will kill the test-organism in the shortest time is taken as the germicidal value of that substance for the organism used. Both these methods are open to serious sources of error, particularly in the testing of powerful germicides. In Sternberg’s method, small quantities of the substances