PLAGUE VACCINES 399 



products seem to be mainly intracellular, but the broth 

 itself is not without action. 



Other vaccines have also been devised. Lustig and Galeotti 

 prepared one by digesting the growth from agar cultures with 1 per 

 cent, caustic soda solution, filtering through paper, and precipi- 

 tating with very dilute acetic or hydrochloric acid, or by saturation 

 with ammonium sulphate. The precipitate is dissolved 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 used only with the greatest caution. 



Klein 1 has 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. 



With reference to experimental immunity and protection in 

 plague, Klein 2 found that a guinea-pig which had been three times 

 injected with an amount of living culture insufficient to kill was 

 still capable of being infected ; that the blood of a guinea-pig which 

 had twice passed through an attack of plague did not contain an 

 appreciable amount of germicidal substances ; and that the im- 

 munisation of guinea-pigs by sterilised cultures is an extremely 

 slow and difficult process. Calmette also found that the guinea-pig 

 was extremely difficult to immunise. 



Calmette, from laboratory experiments, surmised that protection 

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

 susceptibility to infection is increased. These observations are not 

 borne out in practice, for Bannerman 3 found that so far from there 

 being an increase in mortality among those who have been inocu- 

 lated and who develop plague within ten days of inoculation the 



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



2 Ibid. 1896-97, App. B., p. 2. 



3 Centralbl. f. Bakt- /l te Abt.). Bd. xxix, p. 873 (Bibliog.). 



