256 Arthropods Transmission of Disease 



Knab's article should serve a valuable end in checking irrespon- 

 sible theorizing on the subject of insect transmission of disease. 

 Nevertheless, the principles which he laid down cannot be applied 

 to the cases of accidental carriage of bacterial diseases, or to those 

 of direct inoculation of pyogenic organisms, or of blood parasites 

 such as the bacillus of anthrax, or of bubonic plague. Accumulated 

 evidence has justified the conclusion that certain trypanosomes 

 pathogenic to man are harbored by wild mammals, and so form an 

 exception. Townsend believes that lizards constitute the natural 

 reservoir of verruga; and it seems probable that field mice harbor 

 the organism of tsutsugamushi disease. Such instances are likely to 

 accumulate as our knowledge of the relation of arthropods to disease 

 broadens. 



