IMMUNITY AND ANTITOXINS 259 



crops of Kitasato's plague bacillus are grown on ordinary 

 nutritive media plus large quantities of fat. The fat of 

 milk, as clarified butter, is that generally used. Under the 

 globules of fat flakes of culture grow like stalactites, hanging 

 down into the clear broth. These are in time shaken to the 

 bottom, and a second crop grows on the under-surface of the 

 fat. In the course of a month perhaps half a dozen such 

 crops are obtained and shaken down into the fluid, until the 

 latter assumes an opaque milky appearance. This is now, 

 unlike the cholera vaccine, exposed to a temperature of 70° 

 C. , by which the microbes are killed. The culture contains 

 all the toxins, and the dose is 3 cc. This preparation has 

 the advantage of being easily prepared, obtainable in large 

 quantities, and requires no animals in its preparation. 

 When inoculated it produces local pain and swelling at the 

 site of inoculation, and general reactive symptoms such as 

 fever. From a careful analysis of the results of this inocu- 

 lation, it is shown that the efficacy of the prophylactic de- 

 pends upon the virulence of the bacillus culture from which 

 the vaccine is prepared, and upon its dose and ability to 

 produce a well-marked febrile reaction. It appears to be 

 more effective in the prevention of deaths than of attacks. 



The anti-typhoid vaccination is another example of in- 

 oculation to secure active immunity. It is needless, per- 

 haps, to point out that all these vaccinations, except rabies, 

 are prophylactic, and not curative. 



Passive Immunity; Preparation of Antitoxins, We must 

 now consider the question of passive immunity. This, it 

 will be remembered, may be defined as a protection (against 

 a bacterial disease) produced by inoculation, not of the dis- 

 ease itself, as in small-pox inoculation, nor yet of its weak- 

 ened toxins, as in rabies, but of the antitoxins produced in 

 the body of an animal suffering from that particular disease. 

 Examples of this treatment are increasing every year, and 

 the term ** antitoxin " has now become almost a household 



