PRODUCTION OF CHEMICAL POISONS. 163 



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 reproduced 

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

 may be produced by a given bacterium. Thus in diphtheria, 

 for example, the products which produce the local inflammatory 

 reaction and necrosis are in all probability not the same as those 

 which affect the nerve cells and fibres. Further, it is very 

 doubtful whether all the chemical substances formed by a cer- 

 tain bacillus growing in the tissues are also formed by it in 

 cultures outside the body. The separated toxin of diphtheria, 

 like various vegetable and animal toxins (vide infra), however, 

 possesses a local toxic action of very intense character, often 

 producing extensive necrotic change. 



The injection of large quantities of many different pathogenic 

 organisms in the dead conditions 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 "). 



The action of bacteria as mechanical irritants plays a very 

 small part in the processes of disease ; and the differences 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 preducts 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. 



