55 



ears. In these places there is less hair aud grease, affopQing the pests 

 better opportunities of getting at the skin. From these starting-points 

 the scabs spread over the forehead, cheeks, eyelids, and occasionally 

 over the space under the jaw. In badly infected sheep the disease may 

 sometimes extend to the fore limbs, under the belly, around the joints, 

 aud especially between the folds of the knees, hocks, and pasterns. 

 Sheep with coarse dry wool are more likely to suffer this extended 

 invasion than those with fine, oily, and soft wool. Long wool seems 

 to offer a barrier to its progress, for the invasion of parts covered by 

 short wool is much more rapid. The demarkation between the invaded 

 parts of the head and the healthy wool-bearing portions is quite abrupt. 

 In coarse-wooled breeds the disease may rarely cover the entire body. 

 The first indication of the disease is shown by the sheep in rubbing or 

 scratching its head. The intensity of the itching is manifested by the 

 violence of the sheep's action. The fi«st that can be seen on an infected 

 spot is little elevations with soft centers. These elevations break of 

 themselves, or through the rubbing they receive, and from them runs 

 a watery fluid that in drying forms little hard bunches which stick to 

 the skin and adjacent hairs. These little elevations are made by the 

 parasites, which sink themselves into the skin. Here the parasites find 

 suitable food, grow and produce their young. These migrate and pene- 

 trate into the skin as did their parents. Thus the disease. spreads 

 slowly as the parasites increase. Finally, as they become more numer- 

 ous, they cover the invaded skin with a thin layer of scabs. As the 

 disease advances the little scabs not only run together, -forming one 

 mass, but they become thicker, whitened, and hard. Later they run 

 together over the nostrils, lips, face, cheeks, forehead, eyes and ears, 

 and form a dry, hard, thick, scabby mass. By repeated rubbings this 

 scab breaks up, and the skin tears, cracks, and bleeds. Later the 

 wounds heal and scars are formed. When the scabs cover the eyelids 

 the latter close up and the animaLbecomes practically blind, being un- 

 able to find its way or to see food. The insects are to be found in the 

 moist layer underlying the scabs. 



Source of contagion. — ^^The insects which cause the disease have been 

 derived from other sheep with which the recently infected flock may 

 have come in contact, or which may have left a few par9.sites on some 

 brush or stick, or in some trough with which the uninfected flock came 

 in contact. The methods of infection are various, but lie who under- 

 stands that these. parasites always come from some where else, and 

 always from some infected flock, will soon lisarh what to do to prevent 

 his sheep from becoming infected. The variety of Sareoptes parasitic 

 on sheep is similar to the variety living on goats, and it has been ex- 

 perimentally proven that each variety may be transferred and will live 

 on either animal. Some of the varieties living on other animals may 

 be transferred to sheep, but they do not thrive. It is not at all prob- 

 able, therefore, that sheep are infected from other animals than sheep. 



