180 RELATIONS OF BACTERIA TO DISEASE 



chemical products, which act generally or locally in varying degree 

 as toxic substances. The toxic substances become diffused 

 throughout the system, and their effects are manifested chiefly 

 by symptoms such as the occurrence of fever, disturbances of 

 the circulatory, respiratory, and nervous systems, etc. In some 

 cases corresponding changes in the tissues are found, for example, 

 the changes in the nervous system in diphtheria, to be afterwards 

 described. The general toxic effects may be so slight as to be 

 of no importance, as in the case of a local suppuration ; or they 

 may be very intense, as in tetanus; or again, less severe but 

 producing cachexia by their long continuance, as in tuberculosis. 



The occurrence of local tissue changes or lesions produced in 

 the neighbourhood of the bacteria, as already mentioned, is one 

 of the most striking results of bacterial action, but these also 

 must be traced to chemical substances formed in or around the 

 bacteria, and either directly or through the medium of ferments. 

 In this case it is more difficult to demonstrate the mode of 

 action, for in the tissues the chemical products are formed by 

 the bacteria slowly, continuously, and in a certain degree of 

 concentration, and these conditions cannot be exactly repro- 

 duced by experiment. It is also to be noted that more than one 

 poison may be produced by a given bacterium, e.g. the tetanus 

 bacillus (p. 424). Further, it is very doubtful whether all the 

 chemical substances formed by a certain bacillus growing in the 

 tissues are also formed by it in cultures outside the body (vide 

 p. 191). The separated toxin of diphtheria, like various vegetable 

 and animal toxins, however, possesses a local toxic action of 

 very intense character, evidenced often by extensive necrotic 

 change. 



The injection of large quantities of many different pathogenic 

 organisms in the dead condition results in the production of a 

 local inflammatory change which may be followed by suppura- 

 tion, this effect being possibly brought about by certain sub- 

 stances in the bacterial protoplasm common to various species, 

 or at least possessing a common physiological action (Buchner 

 and others). When dead tubercle bacilli, however, are intro- 

 duced into the blood stream, nodules do result in certain parts 

 which have a resemblance to ordinary tubercles. In this case 

 the bodies of the bacilli evidently contain a highly resistant and 

 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 



