237 



IMMUNOLOGY. IMMUNITY AND IMMUNIZING AGENTS 



The several kinds of immunity may be tabulated as follows : 



Racial f^^ observed in the different orders, 



(Phylogenetic) ^^^i'les, genera and species of the 

 [ animal kingdom. 



Immunity 



Inherited 



(Natural) 



Individual 



As observed in dififerent individuals 

 of the same species or variety. (On- 

 togenetic.) 



As observed in the sexes of the same 

 species or variety. 



Induced 



(Acquired) 



Active 



Passive- 



Pathogenetic 

 and environ- 

 mental 



Due to diseases which 

 produce immunity to 

 subsequent attacks 

 as diseases of child- 

 hood; acclimatiza- 

 tion; etc. 



Due to use of modified 

 Artificial | toxins, bacterins, and 



direct inoculation 

 with disease germs. 

 -Use of antitoxins and other disease preventives. 



2. Earlier Theories Regarding Immunity. — Theories have been ad- 

 vanced from tim to time which were intended to explain immunity. 

 Why the individual and racial variation in the behavior towards infections? 

 Why are certain individuals successfully infected while others escape? 

 Why do some of those who are successfully infected die while others 

 recover? Why do the infections (in the cases of recovery) disappear after 

 a time? The following are some of the theories advanced: 



a. Physiological Resistance of the Body Cells. — Some thirty to forty 

 years ago, physicians and physiologists had much to say regarding the 

 variable though inherent property or power possessed by the living cells 

 of the body to resist or ward off infection, the so-called physiological' re- 

 sistence of cells. It was thought that as long as the cells of the body 

 were fully or normally active the infecting agents could not find lodgment 

 therein. This theoretical assumption cannot be gainsaid even at the 

 present time, but unfortunately the theorization says nothing and ex- 

 plains nothing. The theory has no visible means of support. 



b. The Exhaustion Theory. — In order to account ioi the cessation of 

 successful infections in cases of recovery, it was assumed that the infecting 

 agents (bacteria) used up those body-cell substances which were neces- 

 sary to the life of the particular infection. It was thought that these cell 



