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 conceivable 
that infection may occur in this way, it is probable that 
it is the exception and not the rule. 
Yaws (Frambcesia tropica) 
Yaws is a tropical disease, contagious and innocu- 
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 
common in tropical Africa, especially on the west coast, 
