Immunity 557 



anchoring in the stream instead of tying to the dock; by carefully 

 scrutinizing the packages taken from the lighters to see that there 

 are no rats hidden among them; by placitig large metal shields or 

 reversed funnels about all anchor chains, hawsers, and cables so 

 that no rats can climb up from the water in which they are swim- 

 ming at night. Arrangements should also be made for rat destruc- 

 tion on board the ship by means of sulphurous oxid or other poi- 

 sonous vapors to rid the ship of rats before the next port is reached. 

 Passengers and crew should also be kept in quarantine before ming- 

 ling with society. It is much more easy to keep plague out of a 

 port than to combat it when it has entered, for under the latter 

 condition are involved the isolation of the patients in rat-free and 

 vermin-free quarters, the disinfection of the premises and goods 

 where the case arose, and an immediate warfare upon the rats and 

 other small animals of the neighborhood. To emphasize how 

 difficult the latter may be it is only necessary to point out that 

 plague reached San Francisco in May, 1907, during which year 

 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 invented 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 figmres, 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 



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

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



