GERMICIDES. 195 



Some of Rideal's comments (Journal of Tropical Medicine) are as follows: 



In 1897 Kronig & Paul recommended substituting small garnets of uniform size for Koch's 

 thread method, since the garnets could be washed and treated with chemical reagents to neutralize 

 the disinfectants. They tested the results of disinfectants quantitatively by making poured plates. 

 Madsen & Nyman (Zeits. f. Hygiene, Bd. 57, p. 388) and Miss Chick (Journal of Hygiene, February, 

 1908) have shown that their results can be plotted in curves. These show that the velocity of 

 disinfectants depends primarily on number of bacteria to be destroyed, and secondarily on their 

 resistancy or age. 



When anthrax spores are used they may be regarded as of practically the same age and resistance. 

 With ordinary cultures of non-spore-bearing organisms, he states there are individuals of different 

 age having different resistancy, and then the velocity of the disinfectant is not so simple. He says 

 that Miss Chick has shown that by taking cultures of short periods of 3 hours, and sub-culturing, 

 the organisms present in such cultures become uniformly more resistant, and the velocity of dis- 

 infection approximates to the same law governing disinfection of spores. Miss Chick has also found 

 that temperature influences the process of disinfection, disinfection being more rapid in warm 

 climates than in cold ones. Dr. Rideal states that Miss Chick's work has confirmed the method of 

 disinfection recommended by Walker & Rideal in 1903. He says the elaborate method of the use 

 of garnets "may be replaced advantageously by the drop method known under our names." They 

 used carbolic acid as the basis of their tests. Next after the question of standardization of the 

 disinfectants, he considers the culture broth of primary importance. The test organisms should be 

 grown for 24 hours and then inoculated into primary test cultures always made up from nutrient 

 broth of a definite composition. Rideal and Walker have suggested that the broth should contain 

 20 grams of lemco, 20 grams of Witte's peptone, and 10 grams of salt per liter of water, and should 

 after boiling be neutralized with caustic soda, after which 15 cc. of normal hydrochloric acid are 

 added per liter. 



"Having secured a standard broth, standard carbolic acid, and a standard culture, the only 

 other conditions are those of temperature and sterility." 



Rideal says that these and other details are given in a little book by W. Partridge on the " Bac- 

 teriological Examination of Disinfectants," published in 1907 by the Sanitary Publishing Co. He 

 says further: 



" In view of the very great development that has taken place in our knowledge of the constitution 

 of the derivatives of phenol, various refined and highly scientific products have been put upon the 

 market by enterprising manufacturers, and it is, therefore, desirable that the medical man may 

 have a weapon by which these products may be identified and classified according to their germicidal 

 efficiency, not only because these newer products are so valuable in preventing and eradicating disease, 

 but in the comparatively new field of medical application for internal treatment, where, of course, 

 the efficiency of the dose is of supreme importance. 



"Thus, for example, I understand that Dr. Wright and Dr. Morgan in working on cancer are 

 using this test for determining the germicidal value of cinnamic acid derivatives for internal use 

 whilst Dr. Hartigan, in your own Journal in 1905, pointed out that a well known disinfectant with 

 a high coefficient [cyllin, probably] could be used in sprue as an intestinal disinfectant when admin- 

 istered in the form of palatinoids, and Fleet Surgeon MacNab has similarly found that it can also be 

 used internally in treatment of Mediterranean fever. Captain Brodribb has also used the same 

 disinfectant in cantonments in India as a douche for the treatment of gonorrhoea in women." 



In a discussion of this paper Dr. Sommerville referred to the necessity of introducing organic 

 matter into the cultures so that the laboratory tests are in a measure conformed to the actual con- 

 ditions occurring in practice. He says: 



"The question of prime importance is the type and quantity of organic matter which should be 

 introduced. From work executed a year and a half ago, it was found that less than 10 per cent of 

 organic matter brought down the coefficients of all disinfectants to the same figure. Mr. Ainslie 

 Walker and I have recently adopted a i per cent mixture of starch and gelatin." 



Professor Hewlett said: 



"I think that all those who have had anything to do with this Rideal-Walker test must agree 

 with the beautiful simplicity of the method, and I think the greatest credit and congratulations are 

 due to Dr. Rideal and Mr. Ainslie Walker for working out the test. It is really the first practical 

 method that has been devised for comparing the germicidal efficiency of disinfectants. * * * 



"Lastly there is the point which Dr. Sommerville has raised; the test, though so beautifully 

 efficient for so large a number of disinfectants, lacks, of course, in one point, namely, that one is 

 acting upon naked germs, whereas in actual practice the germs are mixed with organic matter. 

 There is a certain lowering of the efficiency of the disinfectant in the presence of organic matter, so 



