146 RELATIONS OF BACTERIA TO DISEASE. 



genie organisms in the dead conditions results in the 

 production of a local inflammatory change which may be 

 followed by suppuration, this effect being possibly brought 

 about by certain substances in the bacterial protoplasm 

 common to various species, or at least possessing a com- 

 mon 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. 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. 



