PRACTICAL APPLICATIONS 403 



have had an extensive trial. Yersin's serum is prepared at the 

 Pasteur Institute, the process being to immunize horses for long 

 periods up to a year and a half by weekly intravenous injections 

 (which do not cause abscesses, as is the case if the injections are 

 given subcutaneously). For the first three months or so dead 

 bacilli are used, afterwards living ones, and a very high degree of 

 immunity is attained. The potency of the serum is estimated by 

 finding the smallest amount which, given twenty -four hours 

 previously, will save a mouse from a lethal dose of living bacilli : 

 this may be as low as 0*02 c.c. Lustig's serum is supposed to be 

 antitoxic as well as bactericidal. It is prepared by the immuniza- 

 tion of horses with a "toxin" prepared by dissolving plague bacilli 

 in i per cent, caustic soda solution, filtering and precipitating with 

 dilute hydrochloric acid. (This has also been suggested as a 

 vaccine.) The precipitate is dissolved in 0-5 per cent, sodium 

 carbonate before use. 



All observers are not agreed as to the efficacy of these sera, but 

 there is a decided preponderance of opinion in their favour. 

 Yersin's serum is most used, and is probably of the greater value. 

 A most important point in connection with its use is that large 

 doses are necessary, and those observers who have not obtained 

 good results have in some cases used quantities which were far 

 too small. Cairns used Yersin's serum in the Glasgow epidemic, 

 and in severe cases gave 150 to 200 c.c., part in the region draining 

 into the affected glands and part intravenously. Choksy, as the 

 result of large experience, urges the importance of a very early 

 use of the remedy, and gives 60 to 100 c.c. for adults and 10 c.c. 

 for infants, giving fresh injections of gradually diminishing amounts 

 every twenty-four hours, until six or eight have been given in all 

 150 to 300 c.c. He used Lustig's serum. In any case the effect 

 of serum is not a great one, a lowering of the case-mortality by 

 about 10 to 20 per cent, being apparently the utmost to be hoped 

 for at present. It appears, however, that no other treatment 

 available is so successful. 



The question of the preventive treatment is much more im- 

 portant. In some cases the serum may be used, and is probably 

 most efficacious ; but its effects are but transitory, and its only 

 legitimate use is to tide the person over the time until vaccination 

 can be performed and active immunity acquired. 



Haftkine's plague prophylactic consists of a virulent broth 

 culture of the bacillus, killed by heat and preserved by the 



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