INFECTION AND IMMUNITY. 561 



her of bacteria that appear upon culture plates from the 

 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 

 bacteria, 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 those particular lesions 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 a 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 are astonished to find that the organs, blood, and 

 tissues generally are sterile, 1 in so far as the presence of 

 the organism with which the animal was inoculated is 

 concerned, and by both cultural and microscopic methods 

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

 tion i. e. y where they were deposited. It is very evident 



1 In by far fche greater number of cases this is true ; but there are 

 isolated exceptions to it. 



