96 INFECTION AND IMMUNITY. 



its being prejudicial to life, and from the danger of spread- 

 ing the infection. 



II. Vaccination, or the introduction of attenuated bacteria, 

 which attenuation is obtained either by submitting the bacteria 

 to a higher degree of heat during their cultivation or by add- 

 ing a small proportion of an antiseptic to their culture-media, 

 or by using bacteria which have grown for a long period of 

 time in artificial media, or by using bacteria which have 

 grown in the bodies of natural immunes. 



III. Intoxication, or the introduction of the toxins of the 

 bacteria in small broken but frequently repeated doses, or in 

 cases where the toxic effect of bacteria is due to substances 

 contained in the cell-body itself by the injection of the dead 

 bacilli. This is the method used for the production of the 

 diphtheria and tetanus antitoxins. 



IV. Antitoxins, or the introduction of bacterial products 

 of any one of the first three processes into other animals, 

 these substances, known by the name of antitoxins, being 

 able to confer immunity to susceptible animals. 



V. By the inoculation of an emulsion of tissues, consisting 

 in the introduction into the animal of the emulsion of certain 

 tissues which are known to be the tissues susceptible to the 

 action of the bacterial poison. 



VI. By introducing into the animal inert particles, such as 

 carmine, mixed with the bacteria. 



Forced immunization of animals consists in introducing 

 gradually and in increasing doses bacterial toxins in sufficient 

 quantity to produce a reaction, but in quantity too small to 

 produce deleterious effects. In this way it has been found 

 that animals immunized produce substances in their tissue- 

 fluids which when inoculated in susceptible animals serve to 

 protect them against the deleterious action of those bacteria 

 or their toxins. 



The Antitoxic and Antimicrobic Blood-Serums. 



The blood-serum of animals used for the purpose of pro- 

 tecting others is said to be antitoxic, when it has been obtained 



