56 CLINICAL BACTERIOLOGY AND 



where we find a mild attack of smallpox was produced 

 by inoculating the discharge from a pustule to ward off 

 dangers of further infection. Following upon this, William 

 Jenner discovered that vaccination with cowpox virus was 

 equally efficacious as a preventive against smallpox in 

 man. This laid the foundation of vaccine-therapy. 



Succeeding Jenner's discovery, the actual cause of certain 

 specific diseases — namely, bacteria — was demonstrated. 

 Then came Koch's work upon the method of isolating and 

 identifying bacteria. 



At a later date Metchnikoff demonstrated his " power of 

 resistance theory," and showed the action of the leucocytes 

 in the lower animal in their endeavours to devour invading 

 bacteria, and this he called " phagocytosis." It was 

 further proved, however, that the serum exercised some 

 specific influence upon bacteria, and it was shown that if 

 the blood-plasma alone was taken the growth of bacteria 

 was inhibited, and on the supposition that there existed in 

 the plasma some protective elements, Buchner gave them 

 the name of " alexins." 



Further, it was demonstrated that an animal suffering 

 from an infectious disease, and recovering, had elaborated 

 within its economy various substances inimical to the growth 

 of the specific bacteria and the creation of their products. 

 These substances appear to be of two distinct kinds : 

 (1) those elaborated consequent upon tissue activities and 

 always present, called non-specific antibodies ; (2) those 

 manufactured in response to an infection, and named 

 specific antibodies. 



These antibodies vary in character and action, and at 

 the present time little is known about them. 



The following are some of the principal antibodies : 



Antitoxins. 



These are specific bodies which counteract poisons, or 

 toxins, manufactured within the animal body by disease- 

 producing organisms. 



