Diseases of cattle, sheep, goats Diseases of cattle, sheep, goats and swine diseasesofcattle00mous Year: 1920 432 DISEASES OF THE BLOOD. Etiology. Depressing and weakening influences of all kinds have been blamed for producing the disease, but the general consensus of opinion points in the direction of infection with micro-organisms carried and introduced into the sheep's system by the common sheep tick or ' grass tick ' {Ixodes reduvius). The following remarks on, and illus- trations of, this parasite are from an article by Mr. Wheeler, of Alnwick {Vetcrinanan, Vol. LXXIII., No. 867, p. 141
Diseases of cattle, sheep, goats Diseases of cattle, sheep, goats and swine diseasesofcattle00mous Year: 1920 432 DISEASES OF THE BLOOD. Etiology. Depressing and weakening influences of all kinds have been blamed for producing the disease, but the general consensus of opinion points in the direction of infection with micro-organisms carried and introduced into the sheep's system by the common sheep tick or ' grass tick ' {Ixodes reduvius). The following remarks on, and illus- trations of, this parasite are from an article by Mr. Wheeler, of Alnwick {Vetcrinanan, Vol. LXXIII., No. 867, p. 141). Life History of the Grass Tick. Sheep ticks (which must not be confused with the sheep-ked, or keb, a wingless six-legged fly, universal on sheep everywhere) are allied to the spiders. They pass through four stages of existence: the egg—the six-legged larva—the eight-legged pupa—and, finally, the eight-legged adult male or female. In each of the three stages of larva, pupa, and adult female, all Fig. 200.—Adult male of the grass tick. Length, th of 1 inch.
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