58 



little white points with ri brownish extremitj^ If picked up by the 

 point of a knife or a sharp stick and i)hiced on tlie hand tliey will be 

 seen to move. The six-legged young, the eight legged adults, the 

 sexes, couples joined together, aud the eggs of this interesting insect 

 can easily be identified by the aid of a low-power magnifying glass. 



Prognosis. — The disease is favored in its advance by the seasons in 

 which the wool grows longest, and in which the sheep are brought into 

 closer contact in sheds. Autumn and winter are the most favorable 

 for its spread and rapid advancement. In summer, and especially after 

 shearing in spring, the disease makes little, if any, headway until the 

 wool has grown to a considerable length. -Age, temperament, state of 

 health, energy, and race of the animals, the length, fineness and abun- 

 dance of fleece, and the hygienic surroundings have much influence on 

 the advance, progress, and termination of the disease. The young, the 

 weak, the closely in-bred, the long coarse-wooled sheep, and those sub- 

 jected to bad climate, to unhealthy localities, to poorly constructed, illy- 

 ventilated sheds, are all more subject to the rapid advances of the 

 disease. On the other hand, healthy, well-fed, well-housed sheep may 

 withstand the ravages of the disease for months. 



When left to itself scab causes severe disturbances of the functions 

 of the skin, and on account of the intense itching brings on fatigue, 

 through loss of rest and sleep. Marasmus and cachexia preceding, 

 death may come to weak, ill-nourished subjects in two or three months. 



The mortality due to scab varies much, depending on the season, gen- 

 eral health of the flock, food, shelter, aud a variety of other factors. It is 

 mostdisastrous in autumn and winter among sheep poorly fed and housed, 

 and of weak constitutions. Many other diseases may intervene aud carry 

 off the weakened animals. The death-rate is not the only occasion of 

 loss, for whether the shepherd keeps his flocks for mutton or wool he 

 will find a loss in either, depending much on the severity of the dis- 

 ease. Ewes weakened by the disease will remain infertile, abort or pro- 

 duce but weak aud feeble lambs, which will either die or scarcely be 

 worth the i^eariug. To this loss must be added the decreased value of 

 the wool obtaiucd from the first sliearing after a recovery from the at- 

 tack, duo to the mixing of the ends of the old wool with those of the 

 new, known as the double ended wool. This mixture lessens the value 

 for manufacturing purposes. 



Source of contagion, — Remembering that common scab is caused by 

 insects which the infested flocks are continually spreading broadcast 

 by dropping tags of wool by the wayside, by leaving them attached to 

 brush, by rubbing posts aud fences, it is easy to realize that there are 

 many methods of transmitting the malady. Experiments with these 

 insects have shown that they can live at a moderate temperature on a 

 piece of scab from ten to twenty days; that they may live after being 

 subjected to intense cold; that they die more rapidly when they are in 

 contact with animal matter at freezing temperature, and that they die 



