180 KELATIONS OF BACTERIA TO DISEASE 



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 pyaemia ; 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 con- 

 centration, and these conditions cannot be exactly reproduced 

 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. 429). 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. 188). The separated toxin of diphtheria, like various vege- 

 table 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 

 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. 



