662 ACTIVE IMMUNIZATION 



constitutes the main principle, and causes the production of an anti- 

 toxin as its main antibody; with other bacteria, such as the typhoid 

 bacillus, a soluble toxin and an endotoxin in combination with the protein 

 of the bacterial cell are probably the main antigenic factors responsible 

 for the formation of a bacteriolysin, opsonin, antitoxin, agglutinin, etc. 



In brief, the antigenic principles of a microorganism are mainly 

 thermostabile and fairly resistant substances, so that a bacillus may be 

 so attenuated or altered that it cannot multiply or produce disease, and 

 yet is capable, through the agency of substances that have escaped 

 destruction, of causing the production of specific antibodies. 



As was previously stated, vaccines may cause the production of 

 different antibodies. As curative agents, however, it would appear that 

 they are most efficacious in those infections in which phagocytosis is 

 known to be chiefly concerned in the defense of the host, e. g., in staphy- 

 lococcus infections. As shown by Wright and Douglas, Neufeld and 

 Rimpau, a bacterial vaccine facilitates phagocytosis, not so much 

 qualitatively or quantitatively as through the production of specific 

 substances that act directly and primarily upon the bacteria and render 

 them more vulnerable to phagocytosis (opsonin or bacteriotropin). 

 Wright has advised a method of opsonic measurement, previously 

 described, for measuring the immunity response, but, as will be under- 

 stood, while the opsonin may be the chief antibody, it is seldom if 

 ever the only one, so that the opsonic index is but one measure of de- 

 fensive power. 



According to Vaughan, a microorganism is directly responsible for 

 the production of a specific proteolytic ferment capable of causing the 

 disintegration or destruction of the bacterial cell and its products. The 

 ferment is the antibody, and is produced during an infection or by a 

 vaccine in just the same manner as antibodies in general are produced. 

 In other words, Vaughan regards antibodies as of the nature of pro- 

 teolytic ferments; thus the protein of the microorganism composing 

 a vaccine produces a specific proteolytic ferment capable of overcoming 

 its substratum when it meets the latter in the form of the invading 

 microorganism of an infection. 



For example, the tissues affected may be unable to produce a suffi- 

 cient quantity of the specific ferment necessary to overcome the infec- 

 tion. The injection of bacterial protein in another and healthier part 

 of the body leads to the production, in this locality, of a specific ferment 

 that is conveyed to the diseased area by way of the circulatory system, 

 and aids in destroying the protein of the infecting microorganism and its 

 tissues. 



