Sheep-Scab. 



347 



injury to the skin, which is followed by an exudation of serum 

 and the formation of crusts or scabs, under the edge of which 

 the parasites and their ova are to be found. 



As the acari or mites increase in number they move from 

 beneath the scabs to the more healthy parts of the skin, and 

 thus extend the area of the disease. 



The injury to the skin produced by these mites is followed 

 by falling of the wool, and the fleece becomes broken and 

 tufted, or matted together, giving the animal a ragged 

 appearance. 



As soon as a sheep is found to present the above symptoms 

 the owner should at once examine the animal, and, if he has 

 any doubt as to the nature of the disease, call in the assist- 

 ance of his veterinary adviser to discover whether the itching 

 and rubbing are due to the presence of the Sheep-Scab or 

 another parasite, or other causes. 



{Magnified 2q0 diameters.) 

 Figure 1. — Sheep-Scab Acarus. 



The most convenient method of examining a piece of wool 

 or crust taken from a suspected case of scab is to spread it 

 out upon a dark surface and place it in the sun or any other 

 warm position, when the acari will be seen as small white 

 specks moving about on the wool or perhaps on the surface 

 beneath it. These moving- objects should then be examined 

 with a pocket lens or with a microscope having an objective 

 of low power (one inch will be sufficient;, when the para- 

 site and the ovum will present the appearances seen in 

 Figure i. 



The parasites and the ova are usually abundant in the 



