INFECTION AND IMMUNITY. 455 



blood and internal organs, and in a lessening in the 

 amount of mechanical obstruction offered to the circu- 

 lation through plugging of the capillaries by masses of 

 bacilli, as detected by microscopic examination of sec- 

 tions of the organs; indeed, this latter condition may 

 often have almost, if not quite, disappeared. We see 

 here an animal dead from the invasion of the same 

 organism that produced death in the first animal, but 

 with little or none of the appearances to which we were 

 inclined to attribute the death of that animal. It is 

 apparent, then, that this organism with which we have 

 been working can destroy the vitality of an animal in 

 a way other than by mechanically obstructing its blood- 

 vessels; it possesses some other means of destroying 

 life. Possibly its growth in the tissues is accompanied 

 by the production of soluble poisons, which when pres- 

 ent in the blood are not compatible with life. 



Let us see if the study of another group of infections 

 will furnish any evidence in support of such an hypoth- 

 esis. Introduce into the subcutaneous tissues of a 

 guinea-pig a small amount of pure culture of the bacil- 

 lus of diphtheria. In three or four days the animal 

 dies. We proceed with our autopsy in exactly the same 

 way that we did with the animals dead of anthrax, and 

 will be astonished to find that the organs, blood, and 

 tissues generally are sterile,^ in so far as the presence of 

 the organism with which the animal was inoculated is 

 concerned, and by both culture and microscopic methods 

 it is possible to detect them only at the site of inocula- 

 tion, where they were deposited. It is very evident 

 that we have here a condition with which mechanical 



1 In by far the greater number of cases this is true, but under particular 

 circumstances there are exceptions. 



