capable of transmitting the infection. The proportion of infected ticks in natural conditions is small; only 1 in 296 in Ricketts' experience.

In conformity with the seasonal prevalence of the tick, the disease in man is commonest in April, May, and June.*^[1]

Treatment and prophylaxis.— In the absence of a specific remedy, treatment must be conducted on general principles, having regard to the natural history and nature of the disease. Attempts at prophylaxis are now being carried out, based on the above-described hypothetical method of transmission of the disease. War is being waged on the ground squirrel and the woodchuck; domestic stock and goats are being systematically dipped to prevent the spread of and, if possible, to exterminate the tick.

Fricks, finding that if D. venustus is placed on the fleece of an unshorn sheep it either dies or remains unimpregnated, and is manifestly on an uncongenial host, has suggested, in addition to the measures just mentioned, turning the badly infected districts into sheep-runs.

1. ↑
   • Tick paralysis.— According to Hadwen, the tick,
   D. venustus, as it occurs in the dry district of British Columbia, Keremeos, gives rise to a peculiar form of paraplegia in sheep which, directly or indirectly, may prove fatal. In the same district it affects man and other animals in a similar way. Todd has called attention to this disease, of which he has collected a considerable number of cases, some of them fatal. Nuttall, working in Cambridge, England, has confirmed Hadwen's experiments. He placed one of the ticks received from Hadwen on a healthy dog. Twelve days afterwards the dog became completely paralysed in fore- and hind-legs. Ultimately it gradually recovered. This form of tick disease is manifestly different from Rocky Mountain fever, as it is non-febrile, is unattended with eruption, and is not communicable by inoculation. Possibly it is produced by a poison instilled by the'tick during haustellation. The wound it makes is very painful, is attended with œdema and, on forcible removal of the tick, with free bleeding as if some anticoagulin had been introduced. In sheep the favourite points of attachment of the tick are on the back along the course of the spine; in man, the nape of the neck. A somewhat similar form of paralysis is described by Eaton as following on tick bite in Queensland, Australia, the incriminated tick being Ixodes ricinus. Bancroft reports from the same country a similarly caused form of epileptiform convulsions in cats and dogs.