54 PATHOGENIC BACTERIA. 



entrance into an animal, grows with great rapidity, 

 completely blocking up the blood- and lymph-channels, 

 so that the proper circulation of these fluids is stopped 

 and disease and death must result. Perhaps more com- 

 mon than this is a local establishment of the organisms, 

 with a resulting inflammation, due partly to the presence 

 of the foreign organisms, and partly to their toxic me- 

 tabolic products. More often, however, the pathogenic 

 bacteria produce powerful metabolic poisons toxins, 

 ptomaines, etc. which either cause widespread destruc- 

 tion of the tissues immediately acted upon, or, circulating 

 throughout the organism, produce fever, nervous excita- 

 tion, and a general overthrow of the normal physiological 

 equilibrium. These peculiarities serve to divide the bac- 

 teria into 



Septic bacteria, 

 Phlogistic bacteria, 

 Toxic bacteria. 



The bacteria of suppuration probably act in several 

 ways. Their products may be of a violently chemotactic 

 nature, or their virulence, exerted upon the surrounding 

 tissue, may destroy large numbers of the cells, whose 

 dead bodies may be chemotactic. When the suppura- 

 tion is violent the toxic product of the bacterium is itself 

 most probably strongly chemotactic. 



How the disease-producing bacteria effect their en- 

 trance into the tissues is an interesting question. The 

 channels naturally open to them are those leading into 

 the interior of the organism, and must be separately con- 

 sidered. 



(a) The Digestive Tract. Attention has already been 

 called to the facility with which the bacteria enter the 

 digestive tract in foods and drinks. Once their metabo- 

 lism is in active progress, the poisons which they produce 

 are ready for absorption. It seems probable that the 

 absorption of the toxic substances by reducing the vitality 

 of the individual predisposes to the formation of local 

 lesions through which the bacteria may enter the intes- 



