NON-SPORING BACILLI 261 



effects. These endotoxins are comparatively resistant to 

 heat', being unaffected by exposure to 65 C. for one hour. 

 By the injection of these endotoxins in suitable doses, a 

 degree of immunity against living virulent bacilli is 

 obtained. The serum of such immunized animals is found 

 to confer a degree of protection on small animals. 

 Immunization. 



1. Preventive inoculation. Haffkine's method. Cultures 

 are made in flasks, with oil drops on the surface. Stalactite 

 growths form, and the flasks are shaken every few days 

 to break those formed, and so induce fresh crops. The 

 incubation temperature is 25 C., and six weeks' growth 

 is allowed. Thereafter the culture is sterilized by heating 

 for one hour at 65 C., and carbolic acid is added to make 

 the bulk contain 0-5 per cent. The contents are well 

 shaken to distribute the sediment, and then bottled for 

 use, the fluid thus containing the dead bodies of bacilli as 

 well as any toxins that may be in solution. It is 

 administered subcutaneously, and usually in one dose of 

 5 c.c. The susceptibility is said to be reduced to one- 

 fourth, and the mortality among those inoculated who 

 take the disease is about one-half of that among the 

 non-inoculated. Protection begins a few days after inocu- 

 lation and lasts for several months. 



2. Anti-plague Serum. Yersin has prepared a serum 

 from horses, by injecting dead bacilli into the sub- 

 cutaneous tissues, then into the veins, and finally, living 

 bacilli intravenously. After a time, blood is drawn off, and 

 the serum preserved in the usual way ; 10 to 20 c.c. are 

 injected daily. Some curative power has been observed. 



Serum Diagnosis. Specific agglutinins appear in the 

 blood of some patients, but the potency of the serum is 

 not strong, and the test is not easily carried out, owing to 

 the tendency of the bacilli to adhere in clumps preventing 

 a satisfactory emulsion being got. Hence the macroscopic 

 or sedimentation method is preferable. Cairns, in the 

 Glasgow cases, found that the reaction appeared about a 

 week after onset of the illness, increased until the sixth 

 week, and then faded away ; being most marked in severe 

 cases taking an early and favourable crisis, less in severe 

 cases tending to a fatal issue, and feeble or absent in the 

 mild cases. The best dilutions were i-io to 1-50. 



