LOUPIXG-ILL. 



000 



comfort. It was, however, noticed that when they were very 

 numerous on lambs, such lambs presented the disease in an 

 aaaravated form, as if the dose of the disease-inducinsj material 

 had been a strong one. The belief in the influence of the tick, 

 or its close connection with the disease, being so general, it was 

 necessary to consider this point very carefully, with the view of 

 determining if any relationship existed between the parasite 

 and the disease. The result of observations on this point was 

 confirmatory of the popular idea ; for it was found — 1st. That 

 where louping-ill existed there the tick -was sure to be : 2d. That 

 where the parasites were absent there was no louping-ill ; and 

 it is a remarkable fact that upon ground having a westerly or 

 southern aspect ticks and louping-ill prevail, whilst on adjoining 

 grounds with easterly or northerly aspects, upon which the 

 grasses are short, thus providing no cover for the ticks, the 

 disease is rare : od. That the appearance of the parasites on 

 the sheep in April and early summer was concomitant with the 

 annual outbreak of the disease: 4:tJi. That in Skye, where it is 



Fig. 29.— The Tick. 



said the disease appears both in spring and autumn, the tick 

 being also there in autumn as well as in spring. 



Ticks are occasionally found on land free from louping-ill. 

 From this it must be concluded that the parasites are the 

 conveyers or inoculators of a virus. By improvement of the 

 land by ploughing and liming, by artificially feeding the sheej), 

 and destroying or otherwise disposing of old grasses — the natural 



