PREVENTIVE MEDICINE 357 



Arsenious acid in from a to a 1 per cent, solution did not kill mites 

 exposed to its action for twenty hours. It is frequently stated, 

 chiefly by laymen, that mange parasites can live in an empty stable 

 for months, and that if a stall that has held a mangy horse be 

 vacated for as long as six months it is still infective. Mange 

 parasites have been credited with the power to lie dormant in 

 crevices in the stall divisions for an almost indefinite period, and 

 to this many have attributed the periodic outbreaks that undoubtedly 

 do occur in some stables. It is more probable that the horses have 

 never been properly cured and that a few parasites remain more 

 or less quiescent on their skin, to resume activity when the conditions 

 of the skin and other predisposing factors are favourable to them. 

 Nevertheless it would be the height of folly to rely upon natural 

 disinfection to rid a stable of the nuisance; vigorous disinfection 

 should be employed. The viability of the mange parasite away 

 from its host is a question having great importance from a legal 

 point of view. 



Period of Incubation. Not much is known as to the time that 

 elapses between infection and the symptoms that the mites have 

 obtained a hold on their host. Schumann* experimented on two 

 horses with the sarcoptic mange mite and concluded that with 

 long-haired horses the incubation period lasted seventeen days and 

 twenty-four days where the hair was shorter. Long winter hair, 

 perhaps, affords more favourable conditions for the parasites. 



The Effects of Mange Infection. A pruritus of varying intens- 

 ity accompanies mange infection. This is due to juices of an irritat- 

 ing nature secreted by the mites and not to the mechanical actions 

 of biting, sucking or crawling. The intensity of the prurigo is 

 most marked with psoroptes and least with chorioptes, sarcoptes 

 being between the two. The irritation is worse in the stable than 

 in the open air owing to the warmth increasing the activity of the 

 mites; for the same reason the application of a rug on the horse 

 causes him to bite and tear at the body with increased vigour. If 

 neglected, the parasites spread practically over the whole animal 

 and the irritation gets so severe and constant that the unfortunate 

 animal gets no rest, consequently it fails to thrive, becomes cachectic 

 and 'eventually dies. Psoroptic mange may, however, remain con- 

 fined to the tail for long periods. Emaciation is not a cause but 

 a result of mange infestation. Starvation, bad stable management 

 and mange often go together, but mange may be found on occasion 

 where the management of the stable is good and the food excellent. 



Sheep scab (see page 365) causes loss of condition of the sheep, 

 * Deutsche tierarztl. Wochenschr, XXIV., p. 194, through Vet. Rev., I., p. 86. 



