TISSUE CHANGES PRODUCED BY BACTERIA 155 



slowly acting substance which gradually diffuses around and 

 produces effects (vide Tuberculosis). 



Summary. We may say then that the action of bacteria as 

 disease-producers, as in fact their power to exist and multiply in 

 the living body, depends upon the chemical products formed 

 directly or indirectly by them. This action is shown by tissue 

 changes produced in the vicinity of the bacteria or throughout 

 the system, and by toxic symptoms of great variety of degree and 

 character. 



We shall first consider the effects of bacteria on the body 

 generally, and afterwards the nature of the chemical products. 



EFFECTS OF BACTERIAL ACTION. 



These may be for convenience arranged in a tabular form as 

 follows : 



A. Tissue Changes. 



(1) Local changes, i.e. changes produced in the neigh- 



bourhood of the bacteria. 



Position (a) At primary lesion. 

 (6) At secondary foci. 



Character (a) Tissue reactions ) Acute or 



(b) Degeneration and necrosis j Chronic. 



(2) Produced at a distance from the bacteria, directly or 



indirectly, by the absorption of toxins. 



(a) In special tissues 



(a) as the result of damage, e.g. nerve cells and 



fibres, secreting cells, vessel walls, or 

 (/3) changes of a reactive nature in the blood- 

 forming organs. 



(&) General anatomical changes, the effects of mal- 

 nutrition or of increased waste. 



B. Changes in Metabolism. 



The occurrence of fever, of errors of assimilation and 

 elimination, etc. 



A. Tissue Changes produced by Bacteria. The effects of 

 bacterial action are so various as to include almost all known 

 pathological changes. However varied in character, they may 

 be classified under two main headings : (a) those of a degenera- 

 tive or necrotic nature, the direct result of damage, and (6) those 



