TICKS 171 



names. Heartwater in sheep is a form of piroplas- 

 mosis. Horses also suffer, and the malignant jaundice 

 or bilious fever, which makes it impossible to keep 

 dogs in certain parts of this country, is also caused by 

 a Piroplasma. Finally, under the name of Rocky 

 Mountain fever, spotted or tick fever, the disease 

 attacks man throughout the west half of the United 

 States. 



The organisms which cause the disease live for the 

 most part in the red blood-corpuscles, but they are 

 sometimes to be found in the plasma or liquid of the 

 blood. Unfortunately, we know but little about the 

 life-history of the Piroplasma, or of the various stages 

 it passes through, but we do know how it is trans- 

 mitted from animal to animal and from man to man. 



We have seen that the carrier or 'go-between' in 

 the case of the malaria is the mosquito, and in the case 

 of the sleeping-sickness is the tsetse fly. The Piro- 

 plasma, however, is not conveyed from host to host by 

 any insect, but by mites or ticks, members of the large 

 group of Acarines, which include beside the mites the 

 spiders, scorpions, harvestmen, and many others. 



The ticks differ from the insect bearers of disease 

 inasmuch as the tick that attacks an ox or a dog does 

 not itself convey the disease, but it lays eggs for 

 I regret to say here, as with the Anopheles, it is the 

 female only that bites and from these eggs arises the 

 generation which is infective, and which is capable of 

 spreading the disease. The tick which conveys the 

 Piroplasma from dog to dog is called Hcemophysalis 

 leachi. The brilliant researches of Mr. Lounsbury 

 have shown that even the young are not immediately 

 capable of giving rise to the disease. The female tick 

 gorges herself with blood, drops to the ground, and 

 begins laying eggs. From these eggs small six-legged 

 larvae emerge. These larvae, if they get a chance, 

 attach themselves to a dog, gorge themselves, and 



