44 VACCINE AND SEBUM THEEAPY 



immunity it is necessary to introduce the specific 

 virus into the animal to be immunised. 



At the same time, it is evident that to introduce 

 the infective material into an animal by the same 

 channel as that by which infection enters in the natu- 

 rally acquired disease would merely induce the very 

 conditions from which it is sought to gain protection. 

 Some other method must be selected. Several 

 different ways of inoculation without conveying an 

 actual attack of the disease are available : 



1. By use of attenuated virus. 



2. By using the dead bodies of the bacteria. 



3. By inoculating the bacteria in some special 

 way, different from that by which they normally 

 enter the body to cause infection. 



4. By the injection of an antitoxic serum at the 

 same time as the injection of virulent organisms is 

 made. 



5. By inoculating a very small number of virulent 

 germs. This is the method now used to protect 

 against rabies. 



6. By sensitising the bacteria before inoculation. 

 This is accomplished by mixing the bacterial emulsion 

 with its heated specific antisera and allowing the 

 mixture to stand for twelve hours. 



7. Prenatal immunisation. This is a method 

 which has been very little used, if at all, in this 

 country. It consists of immunising the foetus, 

 through the maternal blood — that is, the pregnant 

 mother is inoculated with the specific virus of the 



