CARRIAGE OF DISEASE 165 



animals to sterilized culture plates. It seems perfectly 

 demonstrated that flies pick up anthrax bacilli when 

 they walk about and when they feed upon infected ma- 

 terial. It has not, however, been shown how long they 

 may carry the bacillus, and it is not known whether its 

 virulence is reduced by passage through their bodies. 

 Nuttall suggested as early as 1899 that it appears prob- 

 able that non-biting flies, like the house fly, may, when 

 infected, spread anthrax by depositing the bacilli upon 

 wounds or food. 



It may be remarked incidentally that biting flies, such 

 as the stable fly (Stomoxys calcitrans) or any of the 

 gad-flies, biting an animal affected by the disease, might 

 naturally be supposed to carry the Bacillus anthracis 

 into the circulation of a human being by a puncture 

 after a short period, and cases have been reported where 

 malignant pustule apparently followed the bite of some 

 fly. Efforts to prove this by experiment with biting 

 flies and guinea-pigs, however, have not been successful. 

 Nuttall in 1899 concluded that while it is conceivablev^i^,^ ~ 

 that infection may occur in this way, it is probable tn^, ■ - "^^^ 

 it is the exception and not the rule. 



Yaws (Frambcesia tropica) 



Yaws is a tropical disease, contagious and innocii-* 

 lable, characterized by the appearance of papules which 

 develop into a fungus-like, incrusted, and excessively 

 disagreeable eruption. It is widely distributed through- 

 out the greater part of the tropical world, being very 

 com.mon in tropical Africa, especially on the west coast, 



