■238 PAEASITIC DISEASES OF THE SKIN. 



aggravated cases tearing the skin with the hoof, causing ulcer- 

 ation and thickening of the cuticle. 



Cbc Read Scab. 



This disease, as has already been stated, is caused by para- 

 sites called the sarcoptes scabiei. They are the smallest of the scab- 

 forming parasites, being almost invisible to the naked eye. In 

 appearance they are rounded, ovoid bodies, with small pointed 

 proboscis, the full grown parasite having eight legs, four to a 

 side, supplied with suckers or feelers, while the newly-hatched 

 insect possesses only three pair of legs, the other pair appearing 

 about thirty-six hours after birth. 



Location and Sjrniptoms. 



This disease first makes its appearance around the nostrils, 

 rarely on the eyelids, and around the ears. From these locations 

 the scab extends over the whole face, cheeks and eyelids, even 

 to the lower portion of the limbs, under the belly, and especially 

 in the flexures of the knee, hock and pastern joints, wherever 

 the wool is scarce, as this species does not attack the parts covered 

 by the heavy fleece. The first symptom noticeable will be that 

 the sheep rubs and scratches its head violently. On examination 

 at this period, a very small whitish yellow pimple will be found, 

 which, on being rubbed, ruptures, allowing the escape of a yel- 

 lowish serosity. This in drying forms minute crusts, the aggre- 

 gation of which tend to form a thick and hard scab. The 

 vesicles themselves are formed by the parasites burrowing into 

 the skin, where they find the necessary nourishment for their 

 growth and the propagation of the species. The young as soon 

 as they hatch out migrate to a fresh location, where they imme- 

 diately bury themselves in the skin in the same manner as their 

 progenitors. In this manner the disease spreads, slowly at first, 

 but after the first thirty days by leaps and bounds. As the dis- 



