ESSAYS 



327 



however, to inject a larger number of pneumonia germs than about 250,000,000 (at 

 one time), and the amount of immunity conferred by this amount was insufficient 

 to prevent the epidemics. Lately, however, one investigator has boldly inoculated 

 the negroes with doses amounting to 5,000,000,000 pneumococci and upwards, with 

 the result that the epidemics have been stemmed in a very striking manner. 



From data such as the above, as well as from experimental researches on 

 animals, it would appear that large inoculations are necessary if we wish to obtain 

 a certain guarantee of immunity. To solve this important factor, it is obviously 

 necessary to find some means whereby large doses of vaccines may be injected 

 under the skin without harmful results to the individual. 



Attempts have been made in the past to reduce the toxicity of certain germs 

 by growing them on special culture media, or by preparing the vaccine in a certain 

 way before use. The process of " sensitisation," which consists in treating the 

 vaccine with a specific antiserum, has helped to reduce the toxicity in some degree, 

 but on the whole it must be admitted that these attempts have been more or less 

 unsuccessful. 



I believe, however, that now this problem of detoxication of germs has been 

 satisfactorily solved by a chemical process which I was fortunate enough to dis- 

 cover, and which was published in the La?icet on June 28th, 1919. 



This discovery was originally made with regard to the gonococcus (the germ 

 which causes gonorrhoea). About two years ago I was greatly puzzled because 

 the gonococcus, when cultivated artificially, gradually disintegrated and died within 

 a few days. The germ appeared to break up into small granules, a process which 

 is known as " autolysis." After having been baffled for eight months as to the 

 cause of this phenomenon, I eventually discovered that it was due entirely to the 

 chemical reaction of the medium. So long as the medium was acid, no disintegra- 

 tion occurred in the germs ; but, on the other hand, when the medium was 

 alkaline they autolysed very rapidly. In other words, the gonococcus was insoluble 

 in weak acids, but was very soluble in weak alkalis. It was discovered further, by 

 means of a certain delicate test, known as the "complement fixation reaction," 

 that the specific chemical characteristics of the germs were not altered or 

 destroyed by the solvent action of the alkali. 



Later researches showed that, when acid was added to an alkaline solution of 

 gonococci. the bulk of the germ substance was thereby precipitated from the solu- 

 tion. It was also noted that, when the acid precipitate was driven down by centri- 

 fugalisation, the supernatant fluid was extremely toxic, and when injected under 

 the skin it produced all the poisonous symptoms which result from an injection of 

 the actual germs themselves. The acid precipitate, on the other hand, was less 

 toxic than an equal bulk of the germs which had not been chemically treated as 

 above. When the process of dissolving in alkali, precipitating with acid, and 

 removing the supernatant fluid, was repeated about six times, it was found that the 

 supernatant acid fluid became no longer poisonous, and the sixth precipitate was 

 about one hundred times less toxic than an equal bulk of the original germs. 



Picric acid (saturated aqueous solution) proved to be an excellent test for the 

 presence of toxin in the supernatant acid fluid. So long as toxin was present the 

 addition of the picric caused a milky cloud, and when this test became negative 

 the process of detoxication could be considered complete. It was also found that 

 the toxin could be thrown out of solution by the addition of concentrated sodium 

 chloride. This is an important fact, since it points to the necessity of using weak 

 alkali and weak acid in the later stages of the process, since the salt produced by 

 the union of the two reagents might be sufficiently strong to precipitate the toxin. 



