530 VETERINARY HYGIENE 



apply. In Ireland, on the other hand, it is scheduled; 

 very admirable regulations exist to prevent its spread, and 

 moreover to insure it being treated. 



The most common variety of mange in equines is 

 psoroptic, the most difficult to cure is sarcoptic. There are 

 certain conditions favourable to the spread of the disease, 

 of which those most in evidence are exhaustion and 

 emaciation. Of course, the disease only spreads by con- 

 tagion, but the rate of its spread is enormously influenced 

 by debility and want of general care. 



Animals in good condition and those with a clean skin 

 have relative immunity, at any rate from psoroptic mange, 

 though these appear to afford no resistance to the more 

 severe sarcoptic variety. 



Where the parasite exists during the period of non- 

 infection is by no means clear, it may be in the soil, but it 

 is certain that where a body of animals is placed under 

 favourable conditions, the disease appears in the most 

 remarkable way, even when no previous case can be 

 traced. 



There is no reason why the parasite should not live in 

 the soil in the egg state, or even as a mature insect ; we 

 have seen this in the normal habitat of other blood-sucking 

 insects like ticks, which can live for weeks and months 

 without food while awaiting a host. 



It is quite certain that the eggs or the parasite itself 

 may live in other places besides soil, woodwork for example, 

 and be capable of infecting animals. The practical bearing 

 of this is of the utmost importance ; blankets may convey 

 the disease weeks after they have been used for affected 

 cases, while the woodwork of stables, horse fittings on board 

 ship, or railway trucks may harbour the eggs or parasites 

 for a considerable time. 



In fact, if this were not so, it would be difficult to account 

 for outbreaks of disease which occur from time to time 

 without any known direct infection having occurred. 



Psoroptic scabies always spreads rapidly among animals 

 in impoverished condition, but it spreads with extraordinary 

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