UV K. GREIG SMITH. 



i93 



would infect an animal, and other ticks feeding thereon would 

 convey the infection to other animals. ' But it is well known that 

 a mature tick never leaves one host to attach itself to another: in 

 fact, it is generally accepted that it is only in the larval stage that 

 ticks adhere to cattle. The mature and infected tick, therefore, 

 falls to the ground, and under some co\er lays its eggs, which in 

 ti?ne hatch, become the larval forms, and attach themselves to a 

 passing animal with poisonous eflfect. The question, then, comes 

 to be : in what manner is the parasite conveyed from the mother 

 tick to the larval form? Is it carried internally oi- externally? 

 Does the parasite, when absorbed by the tick, pass through the 

 alimentary canal to infect the ground; the exterior of th.e eggs 

 and ultimately the lar^al tick which inoculates the parasite into 

 the animal after the manner of a solid inoculating needle; or does 

 the parasite enter an alternative phase in its life-bistory in the 

 body of the tick 1 One cannot say how the parasite gets from the 

 parent to the larva, but that it certainly does and directly has 

 been proved by the experiments of Theobald Smith and Kilborne, 

 who hatched tick eggs in the laboratory and produced the disease 

 by fastening the larva? on susceptible animals. Prof. Mayo, of 

 Kansas, also produced a fatal attack by placing upon a cow the 

 larvje hatched from mature ticks that had been sent by mail from 

 Texas. These experiments, however, do not decide the question 

 as to whether the parasite exists inside or outside the egg capsule. 

 It would be interesting to know if larva- hatched from disinfected 

 eggs could produce the disease. If they could not, the search for 

 a phase of the parasite in the body of the tick might be useless. 

 Another point worth}- of consideration is whether the tick may 

 not mechanically carry the parasite from the pasture into the 

 animal. We frequently hear of such mechanical inoculation by 

 biting insects such as bugs and gnats, and in the case of louping- 

 ill, a sheep disea.se of Scotland and the North of England, where 

 infection is in all probability carried by the sheep tick, all 

 evidence goes to show that the infection is carried mechanic-all}' 

 by the insect. Theobald Smith considers it to be quite possible 

 that biting oi' stin<rin<)- and V)lood-suckini>- insects may transmit 



