66 THE RELATION OF BACTERIA TO DISEASE 



Principles of Vaccine Treatment. To return for a 

 space to active immunity, it is well to consider here the 

 basis of the present-day bacterin treatment, details of 

 which will be taken up later. The ordinary vaccination 

 against smallpox depends upon the fact that human 

 smallpox virus, passed through a calf for a number of 

 times, loses its power to produce smallpox in man. 

 It does retain power to produce a sore, and this sore 

 contains sufficient of the poison related to smallpox 

 virus to stimulate in the vaccinated person a condition 

 resistant to the virus which would cause true general 

 smallpox. The great Pasteur found that if he heated 

 anthrax bacilli and injected them into sheep these 

 animals became resistant to the disease anthrax. Since 

 the time of Pasteur the management of the process 

 which has been called "active immunization" has 

 been learned. To accomplish this a virus must be 

 treated as was the virus of smallpox, that is, it must 

 be rendered incapable of causing general disease, but 

 it must not be so altered that it has no relation to 

 its original form. The living organisms can be taken 

 and subjected to higher or lower temperatures to those 

 preferred by the individual species, or they may be 

 injected into animals until they will merely live with- 

 out producing disease. This is called reducing viru- 

 lence. They may be killed by heat or obtained in mass 

 and crushed and ground into a pulp. Again, the broth 

 or other material upon which they grow may be used 

 after removing the bacterial bodies by filtering them 

 off through porcelain filters. Having obtained the virus 

 in a reduced state either dead or as active principles, 

 it is injected beneath the skin of the individuals 



