40 PROTOZOA AND DISEASE 



their host's skin and commencing to feed. In some species of 

 ticks, the larvae, having fed, are said to change into eight-legged 

 nymphs whilst still on their host's skin. More often, after about 

 six days, when they have become engorged, they drop off, and 

 undergo their remodelling on the ground. Here, in the course 

 of a few weeks, they * moult ' i.e., shed their skin and are then 

 seen to have changed into nymphs which have four pairs of legs, 

 but no genital apertures. These nymphs require to find a new 

 host to feed upon, and, like the larvae, when engorged they fall to 

 the ground, and there, in the course of a month, undergo their final 

 change into the sexually mature ticks. The vitality of ticks is very 

 striking. Meguin is said to have had examples of Argas Persicus 

 which survived four years' starvation. Nuttall 1 found ticks sent 

 from Africa infected by piroplasmosis were capable of setting up a 

 fatal disease in dogs after being kept without food for seven months 

 in England. The number of eggs laid by the female is said to vary 

 from several to twenty thousand. 



In some cases ticks fed on infected mammals can produce a 

 brood capable of carrying the infection of piroplasmosis in all stages 

 larva, nymph, and adult ; in others the tick is infective only in the 

 stage following that in which the infecting meal was taken. In the 

 case of dogs the adult tick alone appears to be capable of conveying 

 piroplasmosis. 



1 G. H. F. Nuttall, 'Ticks and Tick-transmitted Diseases,' Transactions- of the 

 Epidemiological Society, 1904-1905, vol. xxiv. 



