SCAB IN SHEEP.

Patea Mail, Volume V, Issue 466, 11 October 1879, Page 2

SCAB IN SHEEP.

(Continued from last issue.) The reason that the insect in the first instance is almost always found on the sides of the shoulders, the back, or rump, would seem to be that those are portions of the sheep with which it first comes in contact, either in rubbing against other sheep, or against fences or trees. This feature in the attack of the acari, has also been attempted to be accounted for through the wool on the parts indicated being longer and closer, and more likely to shield them from the cold and light; The insect dislikes going a second time over the same ground in the same attack. Thus, where the disease has been of some standing, and the patches rather large, the skin may have become thin and sound, with a nice crop oi new wool 011 it, on one portion of the patch where the insect had once been at work and caused the wool to fall off; while on another portion of the same patch the skin is bare, thick, and green, and the disease quite active. This is an appearance which is apt to puzzle a person slightly acquainted with scab. Unless the pelt be quite recently taken off the sheep, the live insect can very seldom be detected in it, as they leave it soon after, or, at any rate, when it begins to dry. It is necessary, too, in order to preserve insects intended to be kept f. A examination or experiments (although J they may be placed in locks of wooU, v to put them in a securely corked bottle. . Even in such a position as this they have been found to forsake the wool, and take their quarters and breed in the cork; and it would seem that the instinctive desire which they possess for burrowing whether that be for the purpose of escaping from the light for breeding, or in searching of food —leads the insect to quit those substances in which it cannot carry out this propensity, and take to those in which it can do so. It will thus be seen why infected sheep yards, where there is an accumulation of manure, are so likely to convey the disease, and how necessary it is that where there is much dung it should be burned, for in ground where scabby sheep have been yarded or folded for any length of time, there must be thousands of living acari left in the dung. From what has been said it will be gathered that the fecundity of the scab

Icarus is very great, and both experience and observation go to show that its complete destruction and eradication is very difficult indeed, both on this account and also from its tenacity of life. With respect to its tenacity of life, ■which is the characteristic principally affecting the question of a cure of the disease, in Australia the insect has been known to live for weeks in water, for five or six weeks in a dry sitting-room, and according to Dr Thornton, for nearly three months in a glass case. Not only so, but that gentleman states that insects confined in this way bred and propagated for nearly two years, the one race dying off as the new brood arrived at maturity. It has also been no uncommon occurrence for‘sheep to receive the infection from yards and trees in, which the acari must have existed for several weeks after leaving the scabby: sheep on which they were propagated. In climates, again, such as that of Great Britain, and some of the colder and more upland districts of Victoria and /4^rfv , %)utb Wales, the insects, or their Jps, in favourable situations, live *■ throughout the winter in a torpid state, and become active when the warm weather of spring sets in. In such climates it is advisable to give sheep which bad been cured in the middle or end of sumtner, or during the winter, a precautionary dressing in the following spring. It is questionable how far the ‘insects and their eggs and young which are buried in the skin when sheep are dressed can be reached and destroyed by the dressing. At any rate, all experience goes to show, whether from its being all but impossible to administer a single dressing to a flock of sheep, without some omission or error, or from the insects or their increase being prot 'cted by the scab or by the skin in which they are embedded, a single dressing is not to be relied upon, and the system of dressing a second time at such an interval as would allow the young of the insect, which may be in an embryo state in the skin when the first dressing is administered, to be developed, and on the surface of the skin where the dressing could take effect on them, has been universally adopted to insure success.