28 THE NATURE OF INFECTION 



plication possible. In the case of the diphtheria bacillus similar con- 

 siderations may apply. It must be admitted, however, that mechanical 

 injury is of paramount importance, for we see that the tetanus 

 bacillus, while unable to grow and multiply in structures that are 

 intact, can do so when these have been previously or simultaneously 

 bruised or lacerated. For the reason that the two organisms in 

 question can only exist to advantage in damaged structures, Bail 

 not inappropriately speaks of them as necroparasites (necros dead) . 



