INSECTS AND HUMAN DISEASE 151 



at other times, as in sleeping sickness, the native fauna act 

 in this capacity. That the native fauna and not man 

 himself must be blamed for the survival of verruga is 

 shown by the fact that the disease may be contracted in 

 localities uninhabited by man. What blood-sucking 

 animal, then, under these circumstances, is most likely to 

 be the vector ? Men suffering from the eruptive phase of 

 verruga the infective stage are continuously encountered 

 in the coast regions of Peru, where, however, the disease 

 does not spread, so we may at once dismiss fleas and 

 mosquitoes, which are prevalent in these parts, as well 

 as in the verruga districts ; but the disease does not spread 

 with them. For the same reason, Simulidce or buffalo 

 gnats and horse flies may be excluded, as may also bed 

 bugs and lice. As the chain of evidence is gradually 

 forged the guilt falls more and more upon the invertebrate 

 blood-suckers, the ticks, or upon one of the remaining 

 families of Diptera. Investigations show that the disease 

 is usually contracted at night-time, and ticks bite day and 

 night ; they are so large as to be observed and avoided in 

 the day-time, but at night, while man is asleep, they can 

 feed on his blood for hours without molestation. Again, 

 although the disease may be contracted at almost any 

 season of the year, it is most prevalent in March and April, 

 at the end of the warm, rainy season, and this is the time 

 when the adult ticks are washed down the slopes by the 

 rains, and are found in large numbers, looking for hosts on 

 which to engorge. 



Parasitologists are agreed that the blood parasites 

 causing verruga are allied to Piroplasma, micro-organisms 

 of which some account is given in the chapter on diseases 

 of live stock. All the known species of these blood 

 parasites are transmitted by Ixodince, that is to say, ticks 

 with hard bodies, as opposed to the Argantince, or soft- 

 bodied ticks. It will be seen that there is a close parallel 

 between verruga and Rocky Mountain spotted fever, and 



