TISSUE CHANGES PRODUCED BY BACTERIA. 131 



which produce the local inflammatory reaction and necrosis 

 are probably not the same as those which act on the secret- 

 ing cells of the kidney or on the nerve fibres. 



Further, it may be again stated that the action of the 

 products circulating in the system is often manifested more 

 by symptoms than by tissue changes, though our knowledge 

 of the latter, especially in the nervous system, is gradually 

 being extended. The proportion of tissue change to toxic 

 phenomena varies very widely in the case of different 

 organisms. Leprosy may be mentioned as a disease in which 

 the local lesions may be very widespread, and the number 

 of bacilli enormous, with comparatively little accompanying 

 constitutional disturbances, whilst tetanus is an example 

 which presents quite a converse condition. 



(i) Local Lesions. By this term is meant the changes 

 produced in the neighbourhood of the bacteria. These 

 changes are, on the one hand, of the nature of inflammatory 

 reaction, from the most intense vascular changes in acute in- 

 flammations to the more or less chronic proliferative changes 

 especially of connective tissue, and, on the other hand, of the 

 nature of cell-poisoning, leading to degeneration or necrosis, 

 especially of the more highly-developed elements. They 

 may be roughly classified as acute and chronic changes. As 

 already pointed out, it must be borne in mind that in the 

 case of a given organism, the effects vary in different animals, 

 and further, where the lesion is approximately the same in 

 different animals, differences in their minor characters may 

 be found. Examples of this latter are furnished in the case 

 of tubercle. 



Position of Lesions. In some diseases the lesion has 

 a special site ; for example, the lesion of typhoid fever and, 

 to a less extent, that of diphtheria. In other cases it depends 

 entirely upon the point of entrance, e.g., malignant pustule 

 and the conditions known as wound infections. In others 

 again, there is a special tendency for certain parts to be 

 affected, as the upper parts of the lungs in tubercle. In 

 some cases the site has a mechanical explanation. 



When organisms gain an entrance to the blood from a 



