MODES OF BACTERIAL ACTION. 145 



them, as in tetanus, or a well-marked lesion, as in diph- 

 theria, pneumonia, etc. Or in the second place, they may 

 pass by the lymph or blood stream to other parts or organs 

 in which they settle, multiply, and produce lesions, as in 

 tubercle. 



2. Production of Chemical Poisons. In all these cases 

 the growth of the organisms is accompanied by the forma- 

 tion of 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, con- 

 tinuously, and in a certain degree of concentration, and 

 these conditions cannot be exactly reproduced by experi- 

 ment. 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. 

 The separated toxine of diphtheria, like various vegetable 

 and animal toxines (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 patho- 

 10 



