DISEASES OF SHEEP. 71 



the twelfth day several small spots of a yellowisli-red color, 

 and also a certain thickening of the skin, become per- 

 ceptible, after which a greater or smaller number of knots 

 or bubbles are formed, containing the above-mentioned 

 moisture and producing the scab. After this time the dis- 

 ease takes its regular course. Infection follows sooner or 

 later, according to circumstances. "When a scabby sheep is 

 left among a healthy herd for twelve to twenty-four hours, 

 several of these healthy animals will be most surely in- 

 fected, which infection* or transfer of the mites is done 

 either by immediate contact of the healthy with the dis- 

 eased animal or with other immediate objects, as, for in- 

 stance, when a diseased animal rubs against a fence-pos-t, 

 and shortly afterward a healthy animal, by rubbing against 

 the same post, thereby receives the mites dropped or left 

 by the diseased animal upon the post, such mites retaining 

 their vital and infective power for two or three weeks, ex- 

 cept in a very cold temperature. The disease spreads with 

 great rapidity, especially in warm, wet and sultry weather, 

 and when sheep are kept closely together in stables. Cold 

 and wintry weather, large, free and extensive pastures, 

 cause a considerable delay of the disease.. It always re- 

 quires several months before the larger part of the herd 

 become infected. The further propagation of itch upon the 

 single animal is generally, if not always, caused by the in- 

 crease of mites, which penetrate and deposit their eggs 

 under the upper skin, by which means other generations of 

 mites are produced in a very short period. During warm 

 weather, and especially during sunshine, the mites may 

 be found in innumerable quantities upon the skin ; during 

 cold weather and rain they retire into their abode in the 

 canals under the skin. In some cases sheep itch may be 

 transferred to man, producing a similar scab, but not of 

 such dangerous consequences as genuine human itch : such 



