598 Plague 



there were 156 cases and 76 deaths. Every precaution was taken 

 to prevent its spread, and though the extermination of rats was 

 practised at great expense and with the utmost thoroughness, the 

 disease spread to the ground squirrels and other small rodents, and 

 in 1914 plague-infected rodents were still to be found in the outskirts 

 of the city. 



Immunity .^ — -An attack of plague usually exempts from future 

 attacks. Artificial immunity may therefore be induced in both man 

 and the lower animals by a variety of methods. 



I. Active Immunity. — ^Haffkine* followed his plan of preventive 

 inoculation as employed against cholera, and has devised a method 

 of prophylaxis based upon the use of devitalized cultures. Bouillon 

 cultures are grown in flasks for six weeks; small floating drops of 

 butter being employed to make the "islands" of plague bacilli 

 float. Successive crops of the island-stalacite growth are pre- 

 cipitated by agitating the flasks. In this manner an "intense extra- 

 cellular toxin," containing large numbers of the bacilli is prepared. 

 After testing the purity of the culture by transplantation to agar- 

 agar, it was killed by exposure to 6s°C. for one hour and received 

 an addition of 0.5 per cent, of phenol. The preparation was used in 

 doses of 2 to 3 cc. as a preventive inoculation. A more thorough 

 and prolonged immunity resulted from the administration of a 

 second dose ten days after the first. 



An interesting collection of statistics, showing in a convincing 

 manner the value of the Haffkine prophylactic, is pubUshed by 

 Leumann, of Hubli. The figures, together with a great deal of 

 interesting information upon the subject, can be found in the 

 paper upon "A Visit to the Plague Districts in India," by Barker 

 and Flint, t 



The German Plague Commission J believed that an important 

 improvement in the vaccine could be brought about by the use of 

 the method now generally employed in making bacterio-vaccines 

 {q.v.). They therefore caused the baciUi to grow in Roux bottles 

 upon the surface of agar-agar for forty-eight hours, washed off the 

 bacteria with bouillon or physiological salt solution so that i cc. of 

 the suspension contained about 2 .5 mg. of bacilli, and then heated 

 the suspension for an hour or so at 65°C. After heating, 0.5 per 

 cent, of phenol was added. This mode of preparation has the ad- 

 vantage of excluding the possibihty of the accidental growth of 

 tetanus bacilli and other micro-organisms in the culture. The 

 vaccine appeared to give excellent results in Brazil where it was ex- 

 tensively used. Haffkine, however, considers his method preferable 

 because of the greater quantity of immunizing metabolic products 

 of the bacilh contained in the fluid cultures on account of their pro- 

 longed growth. 



* "Brit. Med. Jour.," June 12, 1897; "India Medical Gazette," 1897. 



t "New York Med. Jour.," Feb. 3, 1900. 



t "Arbeiten aus dem Kaiserl. Gesundlieitsamte," 1899, xvi. 



