TOXINS, IMMUNITY, ETC. 499 



It is administered by subcutaneous injection in the dose pre- 

 scribed. Usually only one injection is made, sometimes two, 

 though the latter procedure does not appear to have any 

 advantage. The method has been systematically tested by 

 inoculating a certain proportion of the inhabitants of districts 

 exposed to infection, leaving others uninoculated, and then 

 observing the proportion of cases of disease and the mortality 

 amongst the two classes. The results of inoculation have been 

 distinctly satisfactory. For although absolute protection is not 

 afforded by inoculation, 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 un- 

 inoculated. Protection is not established till some days after 

 inoculation, and lasts for a considerable number of weeks, 

 possibly for several months (Bannerman). In the Punjab 

 during the season 1902-3 the case incidence among the in- 

 oculated was 1*8 per cent., among the uninoculated 7 - 7 per 

 cent., while the case mortality was 23 - 9 and 60 - l per cent, 

 respectively in the two classes, the statistics being 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, and, finally, living bacilli are 

 injected intravenously. After a suitable time blood is drawn off and 

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

 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- 

 mission, however, came to the conclusion "that, on the whole, a certain 

 amount of advantage accrued to the patients in cases both 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 

 experiments, 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 



