PATHOGEN1CITY OF DEAD BACTERIA. 129 



plasm common to various species, or at least possessing a 

 common physiological action (Buchner and others). When 

 dead tubercle bacilli, however, are introduced 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). It may be here 

 pointed out that there is, however, no relation between the 

 toxic effects of an organism and the extent to which it 

 invades the tissues. Some of the organisms which produce 

 the most highly toxic effects have a comparatively localised 

 sphere of growth in the tissues, and others multiply with 

 great freedom throughout the blood, while their toxic 

 effects in proportion to their number are small. Com- 

 pare, for example, the behaviour of the anthrax bacillus 

 with that of the diphtheria bacillus. But there is, on the 

 other hand, no known example of a bacterium multiplying 

 in the living tissues without producing distinct local or 

 general effects. 



The action of bacteria as mechanical irritants plays a 

 very small part in the processes of disease ; and the differ- 

 ences in their effects, though regulated by the position and 

 rate of growth of the organisms, can be accounted for only 

 by the formation of definite chemical substances which act 

 on the tissues. 



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. 



