CHAPTER XIV. 



Infection and Immunity — Mechanism — Specific Bodies and Reactions — 

 Doctrines in Explanation. 



INFECTION. 



If one examines in detail the lesions resulting from the 

 invasion of the body by the different types of infective 

 bacteria, justification is found for the conclusion that the 

 physical manifestations of infection, that is, the sites of 

 activity and the characteristic lesions, vary with the nature 

 of the different invading parasites. 



To a certain extent this is true; that is to say, the type 

 of lesion characterizing a specific disease is peculiar to that 

 disease and is produced only by the particular micro-organism 

 having the power to excite the disease. But if we take up 

 the various lesions of specific diseases in intimate detail we 

 shall see, as will be shown later, that fundamentally the 

 essential factor in the mechanism of infection is of the same 

 general nature for all diseases, be the characteristic lesions 

 and clinical manifestations what they may; the apparent 

 differences being referable to dissimilarities of structure and 

 function of the various species of bacteria that excite the 

 several phenomena on the one hand, and to the parts of 

 the body of the host that are attacked on the other. Thus, 

 by way of illustration, if we select a group of clinically and 

 pathologically distinct infections, such as anthrax, miliary 

 tuberculosis, and diphtheria, and compare the conditions 

 recorded at autopsy, little of a macroscopic nature will be 

 (248) 



