Trembling in Sheep, etc. 549 



but given the presence of the tick, and of the infection which it 

 carries and the malady might easily be extended indefinitely. It 

 is known to prevail in Northumberland north of the Tyne, in 

 Kirkcudbright, Dumfries, Ayrshire, Lanark, Peebles, Roxburgh, 

 Berwick, Argyle, Inverness, and Ross. In Berwick it is less 

 prevalent than in the other countries named, while in the 

 Western Isles it is not only widely spread rising on the hills 2000 

 feet or as high as the sheep range, but in Skye there are two dis- 

 tinct outbreaks, in spring and autumn respectively, apparently 

 coinciding with the appearance of two successive generations of 

 ticks. This may be due to the prevalence of warm winds from 

 the Gulf Stream. Further investsigation will doubtless show a 

 much wider distribution — the author has' seen an affection bearing 

 the same general characters on the spurs of the Lammermoors in 

 East I/Othian, and the supposed adaptation of the Norse word 

 hloupa (staggering) suggests that it is probably not unknown in 

 Scandinavia. W. Williams notes its prevalence on the Silurian 

 formation, but ticks confine themselves to no geologic stratum, 

 and the tick is the main agent in carrying infection. 



Causes, ist. Sheep Ticks. The sheep tick is not the ked 

 (Melophagus ovinus) which is common on long wooled sheep 

 everywhere and is an example of a wingless, degraded dipterous 

 insect. 



The sheep ticks, on the other hand, are true ixodes, and of the 

 same family with our common wood tick and of the cattle tick 

 (boophilus annulatus) of the Southern States and the West Indies. 

 The ticks collected from the sheep by W. Williams were identified 

 by Mr. Moore, of the British Museum, as ixodes ricinus, ixodes 

 erinaceous and ixodes marginatus. Those obtained by Meek and 

 Greig-Smith showed the following characters : The male is 2.48 

 tnm. long, by 1.30 mm. broad ; the female is 5 to 5.5 mm. long, 

 by 3 mm. broad, or when gorged with blood, 10 mm. long, by 

 7 mm. broad. The fasting female is yellowish green, and when 

 full of blood, blue. Following the rule of their genus, the mature 

 tick has eight legs, the larva but six. The fasting larva _ has 

 head, legs and dorsal plate (scutellum) brown, the remainder of 

 the body yellow. Scattered hairs appear on the body, legs and 

 maxillae. 



In all ticks the rostrum is a characteristic feature. It consists 

 centrally and inferiorly of a dart covered below and on each side 



