SERUM DIAGNOSIS 487 



both the proportion of cases of plague and the percentage 

 mortality amongst these cases have been considerably smaller 

 in the inoculated, as compared with the uninoculated. Protec- 

 tion is not established till some days after inoculation, and lasts 

 for a considerable number of weeks, possibly for several months 

 ( U;iiuu-i man). In the .Punjab during the season 1902-3 the 

 case incidence among the inoculated was 1'8 per cent., among 

 the uninoculated 7 '7 per cent., while the case mortality was 23*9 

 iiiid 60*1 per cent, respectively in the two classes, the statistics 

 U'iiig taken from villages where 10 per cent, of the population 

 and upwards had been inoculated. 



2. Anti-plague Sera. Of these, two have been used as therapeutic 

 agents, namely, that of Yersin and that of Lustig. Yersin's serum is 

 prepared by injections of increasing doses of plague bacilli into the 

 horse. In the early .stages of immunisation dead bacilli are injected 

 subcutaneously, thereafter into the veins, arid, finally, living bacilli are 

 injected intravenously. After a suitable time blood is drawn oft' and 

 the serum is preserved in the usual way. Of this serum 10 to 20 c.c. 

 are used, and injections are usually repeated on subsequent days. 

 Lustig's serum is prepared by injecting a horse with repeated and 

 increasing doses of a substance derived from the bodies of plague bacilli, 

 probably in great part nucleo-proteid. Masses of growth are obtained 

 from the surface of agar cultures, and are broken up and dissolved in a 

 1 per cent, solution of caustic potash. The solution is then made slightly 

 acid by hydrochloric acid, when a bulky precipitate forms ; this is 

 collected on a filter and dried. For use a weighed amount is dissolved 

 in a weak solution of carbonate of soda and then injected. The serum 

 is obtained from the animal in the usual way. Extensive observations 

 with both of these sera show that neither of them can be considered 

 a powerful remedy in cases of plague, though in certain instances 

 distinctly favourable results have been recorded. The Indian Com- 

 mis.sion, however, came to the conclusion "that, on the whole, a certain 

 amount of advantage accrued to the patients both in case of those 

 injected with Yersin's serum and of those injected with Lustig's serum." 

 It may also be mentioned that the Commission found, as the result of 

 t-xperiments, that Yersin's serum modified favourably the course of the 

 disease in animals, whereas Lustig's serum had no such effect. 



3. Serum Diagnosis. Specific agglutinins may appear in the blood of 

 patients suffering from plague, as also they do in the case of animals 

 immunised against the plague bacillus. It is to be noted, however, that 

 in clinical cases the reaction is not invariably present, the potency of 

 the serum is not of high order, and the carrying out of the test is 

 complicated by the natural tendency of the bacilli to cohere in clumps. 

 For the last reason the macroscopic (sedimentation) method is to be 

 preferred to the microscopic (p. 120). A suspension of plague bacilli is 

 made by breaking up a young agar culture in "75 per cent, sodium 

 chloride solution ; the larger ttocculi of growth are allowed to settle, and 

 the fine, supernatant emulsion is employed in the usual way. According 

 to the results of the German Plague Commission and the observations of 

 Cairns, made during the Glasgow epidemic, it may be said that the 

 reaction is best obtained with dilutions of the serum of from 1 : 10 to 



