THEORIES OF IMMUNITY. 



preventive substance existed that would dis- 

 appear under the influence of cold. 



Buchner brought forward a theory to explain 

 the fact of obtaining immunity in the infectious 

 processes. It was based upon the then ac- 

 cepted belief (1877-1883) that a bacterium pro- 

 duced its effects in a localized fashion (that the 

 pneumococcus, for example, could produce effects 

 only in the lung), and also that the inflammatory 

 reaction occurring at the site of growth of 

 the bacteria represented a reenforcement of the 

 local tissues, by the general system. So soon 

 as evidence accumulated that the action of very 

 few bacteria is limited in the way suggested, it 

 became clear that this theory was not sufficient 

 to explain even a small part of the facts observed. 



Various other partial explanations were 

 offered, each lasting only so long as the rapidly 

 growing results of experimentation needed to 

 show their limitations. 



The only ones that have withstood the test of 

 time are those of Metchnikoff, representing the 

 cellular theory, and of Ehrlich, representing the 

 humoral theory. 



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