PLAGUE VACCINES 475 



saturation with ammonium sulphate. The precipitate is dis- 

 solved in a 0-5 per cent, solution of sodium carbonate, and filtered 

 through a Chamber-land filter ; this forms the vaccine fluid. 

 Calmette prepared a vaccine by emulsifying an agar growth in 

 water, well washing the organisms with sterile water to remove 

 adherent toxin, emulsifying again in sterile water, heating to 70 C. 

 for an hour, and finally drying in vacuo. The dry substance 

 can be kept for a considerable time without change. For use 

 1-2 mgrm. are emulsified in 2-3 c.c. of sterile salt solution and 

 injected. 



Yersin proposed vaccinating with living culture of feeble viru- 

 lence, which has been done by Strong in Manila. Though such a 

 method might be used in a plague-stricken district, it is obviously 

 one that can be employed only with the greatest caution. 



Klein l prepared a prophylactic by drying the organs of a 

 guinea-pig dead of plague for three days at 46 C. ; rubbing the 

 material to a powder, and further drying at 37 C. for three days. 

 Of this dry powder 15-16 mgrm. protected a rat, and 25 mgrm. a 

 monkey. 



Calmette, from laboratory experiments, surmised that protec- 

 tion with a vaccine is not attained for some days, and that in the 

 interval susceptibility to infection is increased. These observa- 

 tions are not borne out in practice, for Bannerman 2 found that 

 so far from there being an increase in mortality among those who 

 have been inoculated and who develop plague within ten days 

 of inoculation the reverse is the case, and that in a small com- 

 munity where the population had been partly vaccinated and 

 partly not vaccinated, the incidence of plague during the week 

 following vaccination was less among the vaccinated than among 

 the un vaccinated, pointing to the rapid production of protection. 



Anti-plague serum. This is prepared by growing the 

 B. pestis on the surface of agar in plate bottles, washing 

 off and emulsifying the growth, and for the earlier injec- 

 tions the emulsion is heated to 65 C. for one hour, and 

 the commencing dose is ^V part of a flask. The injections 

 are given intravenously at intervals of a week. At the 



1 Eep. Med. Off. Loc. Gov. Board for 1905-06. 



2 CcnlraMattf. Bakt. (2te Abt.), Bd. xxix, p. 873 (Bibliog.). 



