DISEASES OF THE OX AND SHEEP. 433 



of vegetable food. The creature dies when the cold nights of 

 autumn come on. The gad-fly sucks the blood, while the warble- 

 fly's object is merely to lay its egg or eggs in the suitable 

 hatching-place which is aff'orded by the backs of oxen. Towards 

 Christmas-time, little enlargements appear on the backs about 

 the chine, on the loin, or top parts of the ribs. These continue 

 to increase in size until the spring, and they become half as 

 large, or even quite as large, as a small walnut. About this 

 time the irritation set up is of such a nature that the ox is fain 

 to lick certain parts with some vigour, and this may be taken as 

 a sign that the egg has been hatched. A slight aperture is 

 formed in the skin by means of which the grub can receive air. 

 Towards the end of January, and much more markedly towards 

 the end of February, this opening may be found. 



The breathing apparatus in this fly and other bot-flies is 

 situated at the tip of the tail, and this tip, which is of a blackish 

 colour, can be seen through the opening spoken of. This opening 

 or air-hole through the ox's skin seems to be enlarged by 

 the pressure occasioned by the growth of the larva. The 

 mouth is placed below, and is engaged in feeding upon the 

 ulcerated matter produced by the perpetual suction which the 

 larva keeps up. Towards the beginning of May, the grub has 

 nearly completed its larval state, and at about this time the air- 

 hole is about a quarter of an inch in diameter. In May the full- 

 grown warble, about an inch in length, issues from its hole about 

 mid-day. It presses itself out of the hole, tail first, and falls to 

 the earth, where it finds some shelter, and changes into a chry- 

 salis. It is at first grey, but gradually becomes darker, as this 

 transformation is going on. The outer covering or shell of the 

 chrysalis is very strong, and dark brown or black in colour. 

 About four weeks after the larva has fallen to the ground — that 

 is, at about the middle of June — the fly formed within the shell 

 of the chrysalis frees itself. The female flies become impreg- 

 nated, and shortly afterwards they select a sultry day on which 

 to deposit their eggs in the skin of the back of an ox. Each 

 female fly deposits one or more eggs. 



In order to protect cattle from the attacks of this pest, 

 McDougalFs Carbolic Dressing, as sold in tins, may be dissolved 

 in soft water, in the proportion of two pounds to six gallons of 

 water. This would be sufficient for about seventy-five beasts. 



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