INHERITANCE OF PIROPLA8MA8. 77 



quently reach susceptible hosts, and thus keep the 

 disease alive. Koch, perhaps in dealing with 

 another species of tick (Rhipicephalus decolora- 

 tus), found that hereditary transmission of 

 Rhodesian fever does occur. 



Piroplasmosis of the dog presents still another 

 interesting condition in regard to inheritance in 

 the tick. Neither the larvae nor the nymphs of 

 an infected female are able to produce the disease, 

 but when they reach the adult stage they become 

 infective. It has been assumed that the period 

 between the egg and the adult stage is required by 

 the micro-organism for the completion of its sex- 

 ual evolution, the latter being necessary before it 

 could again become infective. 8 This tick also leaves 

 its host to molt, hence the adults are able to infect 

 new hosts, and from the latter fresh ticks may 

 again become infected. The disease is frequently 

 chronic in the dog as well as in the tick. Motas 

 found that the tick Rhipicephalus bursa, behaves 

 in a similar way in the transmission of piroplas- 

 mosis of sheep. In this instance the tick remains 

 on the host for the first molt, but leaves it for the 

 second. An infected brood is able to transmit the 

 disease only after it reaches the adult stage. 



Christophers has reported still another variation 

 in the inheritance of piroplasmas, in the case of 

 Piroplasma canis in India. The tick concerned in 

 this instance was Rhipicephalus sanguineus, which 

 leaves its host for both molts. The larvae of an 

 infected brood are not virulent, but become so 

 when they reach the nymphal and adult stages. 



8. Experiments by Lounsbury with the tick, Hcemaphy- 

 salis leachi. 



