530 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



cent of the flock. Scab is favored by seasons when the wool is 

 longest, and by huddling or overcrowding the animals; also race, 

 energy, temperament, age, state of health, length, fineness, and 

 abundance of wool, and the hygienic conditions of the surroundings 

 influence the course and termination of the disease. Young, weak, 

 closely inbred animals, and those with long, coarse wool will most 

 quickly succumb. Unhealthy localities, damp climate, and poorly 

 ventilated sheds favor the disease. Pure or mixed Merino sheep 

 succumb sooner than certain other breeds. The mortality varies ac- 

 cording to conditions, but is highest in autumn and winter. When 

 owners are careless the death rate may be very high ; if untreated the 

 sheep may die in two to three months. Hygienic conditions, good 

 food, and cool, dry atmosphere tend to check the disease. Sheep 

 sheds should accordingly be well ventilated and open to light and 

 sunshine. With proper attention to hygienic conditions and thor- 

 ough dipping, a positive cure can be guaranteed. 



Vitality of the Seab Parasite. Taken from the sheep, the mites 

 possess a remarkable vitality. It is generally stated that, kept at a 

 moderate temperature on portions of scab, the adults may live from 

 four to twenty days, but they will occasionally live much longer; 

 cases are on record where they have lived three, four, or even six 

 weeks when separated from sheep; if the atmosphere is dry they 

 will generally die in about fifteen days; but death is often only ap- 

 parent, for the mites may sometimes be revived by warmth and 

 moisture even after six or eight weeks; the fecundated females are 

 especially tenacious of life. Various rather contradictory state- 

 ments may be found regarding their resistance to cold. Krogmann 

 states that they may live at a temperature of 10 C. (+14 F.) 

 for twenty-eight days; other authors claim that the mites die in two 

 hours at 47F.; still other authors, that they die at 50 C. (122F.). 

 They are said to have been kept alive in cold water for six days and 

 in warm water for ten days. Several authors admit, however, that 

 the parasites are usually killed by a soaking rain; though it is 

 claimed that in damp, dark stables they may live for months. Ex- 

 perience has shown that in some cases apparently healthy sheep have 

 become infected in places where no sheep have been kept for four, 

 eight, twelve, or even twenty-four months. 



All matters connected with the vitality of the scab mite have an 

 important bearing in explaining cases of indirect infection on roads 

 over which scabby sheep have been driven, or in fields and sheds 

 where they have been kept. From the facts now at hand, the fol- 

 lowing important rules can be presented : 



(1) Scabby sheep should never be driven upon a public road; 

 (2) sheds in which scabby sheep have been kept should be thor- 

 oughly cleaned, disinfected, and aired, and should be left unused 

 for at least four weeks (better two months) before clean sheep are 

 placed in them; (3) fields in which scabby sheep have been kept 

 should stand vacant at least four weeks (better six or eight) before 

 being used for clean sheep; (4) a drenching rain will frequently 

 serve to disinfect a pasture, but it is well to whitewash the posts 



