6 BIOLOGICAL LECTURES. 



made through such an abscess (Fig. i), which is located, as so 

 commonly happens in experimental cases, in the kidney, the 

 following arrangement is found. The central dark mass repre- 

 sents the bacteria which have been transported hither by the 

 blood current, and which have become lodged in the capillary 

 vessels of the part. Having found here conditions favorable 

 to their increase, they have grown from a microscopic speck to 

 a mass large enough to be seen with the naked eye. As a 

 result of their presence, the surrounding tissue is destroyed, 

 the destruction being recognizable in the specimen by the 

 absence of stainable nuclei in this part. Outside the zone of 

 dead tissue is another in which the cells as compared with 

 those of the healthy tissue at a distance are greatly increased 

 in number. This third zone is the area of leucocytic infiltra- 

 tion, the infiltrating cells consisting of white blood-corpuscles 

 which have passed out of the vessels to accumulate at this spot 

 in answer to what is conceived to be a chemical attraction 

 (chemotropism) exerted by the bacteria and dead tissue. The 

 leucocytes penetrate as far as possible into the dead tissue, 

 and become arrested as soon as the poisonous products of the 

 bacteria are present in quantities sufficient to insure their 

 speedy destruction. Later a solvent action is exerted by the 

 bacteria upon the tissues, causing them to liquefy, and con- 

 verting the contents into " pus," the removal of which leaves 

 a cavity behind. 1 



Certain bacteria are capable of exerting an injurious effect 

 upon tissues and organs of the animal body at a greater dis- 

 tance from their place of localization. Thus, although the 

 diphtheria bacillus often remains localized in the throats of 

 persons suffering from diphtheria, yet very extensive local 

 lesions are found in the near and remote lymphatic glands, in 

 the spleen, liver, heart, nerves, and other organs. These 

 lesions are attributable to the absorption into the body of the 

 toxalbumin, elaborated by the bacteria in the throat. It is 



1 It is not to be concluded that this is the only kind of lesion produced by 

 bacteria. It is a common one, and has been selected for that reason, and also 

 because, as far as known, it is never produced by the action of the toxic products 

 of bacteria alone. 



