CHAPTER XXII 



PARASITES AND DISEASE (VEGETABLE PARASITES) 



Bacteria. We have learned in our study of bacteri- 

 ology that bacteria are an important cause of disease 

 processes. We will now, in pathology, consider the 

 diseases of which they are the cause, and the altera- 

 tions in structure and function of the organs and tissues 

 affected by their growth and multiplication within the 

 body. 



Local Effects Upon the Tissues of Bacterial Growth. 

 The local effects of bacterial activity may be either 

 mechanical or histologic. 



Mechanically, the clumps of bacteria may obliterate 

 small vessels, leading to thrombosis, necrosis, or infarct. 

 By the production of membranes, as in diphtheria, they 

 may occlude the air-passages, causing suffocation. 



The histologic effects of bacterial growth are both 

 proliferative and degenerative. Among the prolifer- 

 ative processes may be mentioned the formation of 

 tumor-like growths, as gumma in syphilis, tubercle in 

 tuberculosis, the nodular formation in leprosy, and 

 the proliferative changes in the vessel walls occurring 

 in late syphilis. Of the degenerative changes, necrosis 

 is the most important, as exemplified in the various ul- 



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