Chapter, XYIII. 



Ectozoa, or External Parasites — Gad-Fly — Lice — Mange — Ringworm — 

 Entozoa, or Internal Parasites — Hoose, Husk, or Verminous Bronchitis 

 — Measles — Tape-Worm. 



ii r I ">HE parasite," says Van Beneden, " is he whose profession it 

 I is to live at the expense of his neighbor, and whose only 

 -*- employment consists in taking advantage of him, b,ut pru- 

 dently, so as not to endanger his life." , Of the parasites which 

 infest cattle there are two general divisions, the external parasites, 

 or ectozoa, which infestthe skin ; and the internal parasites, or ento- 

 xoa, which live within the tissues of the body. 



EXTERNAL PARASITES, OR ECTOZOA. 



THE GAD-FLY. 



During the summer, cattle may sometimes be seen running 

 about the pasture in a state of great excitement, with heads and 

 necks extended, and tails erect and quivering, or rushing in mad 

 haste to the nearest pond or river. (See Fig. 1064.) The cause of 

 this unusual excitement is the gad-fly. (Fig's. 1065 and 1066.) Such 

 is the dread excited among cattle by this fly, that a single one has 

 been known to turn back a herd in spite of, the efforts of its drivers. 

 Young animals and those in good health are usually attacked by 

 the gad-fly, for in them the skin is soft and more easily penetrated. 

 The female punctures the skin of the beast by means of an oviposi-, 

 tor, and deposits in the subcutaneous tissue a drop of acrid fluid, 

 and an egg, which is hatched out by the heat of the animal. A 

 small abscess results, upon the piis of which the larva feeds. Above 

 each larva may be seen a sort of tumor, or ".bump," as Re'amur 

 calls it. (See Fig. 1067.) The presence of these larvae seems to cause 

 no suffering, or at least but very little'. The dread of the fly is probably 

 due to the pain caused by the acrid substance deposited with the egg. 

 In June or July the abscess bursts, and the larva falls to the ground, 

 where it gets under a stone or other object, or buries itself in the 

 earth to prepare for its last transformation. At the end of about 



(808) 



