CHAPTER XVIII 

 BACTERIO-VACCINES 



A BACTERIG-VACCINE is a culture of micro-organisms so modified as 

 to be no longer a source of dangerous infection, and so administered 

 as to stimulate the body' defenses and thus assist either in pre- 

 venting or overcoming more virulent infection. 



The small amount of benefit that occurred from the employ- 

 ment of the Oriental method of "inoculating against small-pox" 

 was based upon the theory that virus of low virulence, obtained 

 from a sporadic case of small-pox if introduced into the healthy 

 body, must result in a mild attack of the disease, by which the 

 individual would be left immune against the more virulent viruses 

 by which epidemics of the disease are brought about. The observa- 

 tion of Jenner, that the virus of cow-pox would protect against 

 small-pox, led to the supposition that the essential causes of the 

 two diseases had originally been the same, but had so diminished 

 that the one became comparatively harmless for man after many 

 generations of residence in the cow. 



The success of Pasteur's preventive inoculation against chicken- 

 cholera depended upon the fact that the bacilli of the disease rapidly 

 lost their disease-producing power when grown artificially in cul- 

 ture-media, though they still retained the power of effecting a 

 change in the fowls which thereafter remained immune. His vac- 

 cination against anthrax was based upon the observation that the 

 spore-forming power and virulence of the anthrax bacillus could be 

 destroyed by cultivation at temperatures beyond a certain point, 

 and that animals infected with bacilli of this modified form subse- 

 quently resisted more virulent infections. His vaccination against 

 rabies was based upon the supposed diminution in virulence that 

 the unknown micro-organisms underwent when exposed to artificial 

 inspissation of the nervous tissue in which they were contained. 

 Such organisms of very low virulence protected against those of 

 higher virulence, and so on. 



From the periods during which these early observations were 

 made, to the present time, when the term " bacterio- vaccine " is 

 in daily use, studies in immunity have been conducted in so great 

 a variety of ways by such a multitude of investigators, that it be- 

 comes tedious to endeavor to trace the logical and orderly steps 

 that lead to present knowledge, theory and practice. Two names, 

 however, stand out conspicuously in connection with the present 

 topic, because of the importance of their contributions, those of 

 Haffkine and Wright. The former used heated and killed cultures 



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