150 INSECTS AND MAN 



well as bed bugs and fleas, occur at Chosica and throughout 

 the greater part of the verruga districts. 



" During the early stages of the work in the building of 

 the Central or Oroya railway up to 1876, when the road 

 was completed into Chicla, thousands and tens of thousands 

 of labourers were employed, largely strong healthy Chilians, 

 as many as eight thousand being carried on the pay roll at 

 one time. During this period the recorded mortality from 

 all causes disease and accident was some seven thousand. 

 A large majority of these deaths were doubtless due to 

 verruga, the result of carrying the road through the 

 verruga district of the Kimac which has given its name to 

 Verrugas Bridge " (Plate XI.). 



It has been shown that verruga cannot be transmitted 

 by mere contact, so long as the skin remains whole, nor 

 can it be contracted through the respiratory or alimentary 

 tracts, under normal conditions. It is a blood disease, and, 

 like all other diseases of this class, can only be transmitted 

 by inoculation. The only way for such inoculation to take 

 place, naturally, is through the bites of some blood-sucker, 

 and to Dr Julian Arce of Lima belongs the credit of first 

 propounding this theory with regard to verruga. As in 

 the case of yellow fever, the causative organism of the 

 disease is unknown, though Barton's bodies are undoubtedly 

 related to the fever phase of the disease, during which 

 phase, by the way, verruga cannot be transmitted by 

 inoculation. In other words, cultures made from blood 

 containing these bodies fail to produce verruga on inocula- 

 tion, so it is probable that they are merely the visible 

 results of a non-infective stage of the organism, which 

 changes to the infective stage, just beneath the skin, 

 thereby giving rise to the eruption. Now we will 

 endeavour to see by what agent verruga is carried from 

 one patient to another. In all such diseases there occurs 

 some natural reservoir for the disease germs ; sometimes, as 

 in malaria and yellow fever, the reservoir is man himself ; 



