128 RELATIONS OF BACTERIA TO DISEASE. 



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 nature of these 

 chemical products and their mode of formation will be 

 afterwards considered, but it may be stated here that they 

 are not, at least in every case, of the nature of simple 

 secretions by the bacteria. They may be formed directly 

 by the bacteria or indirectly by the medium of ferments. 

 A considerable number of the general toxic effects in 

 different diseases can be experimentally reproduced by 

 injection of the products of the organisms obtained from 

 cultures grown outside the body. 



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 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 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 suppuration, this effect being possibly 

 brought about by certain substances in the bacterial proto- 



