■708 DISEASES OF THE SKIN. 



Tliis constitutes the chronic or inveterate stage, and may (as 

 M^quin asserts) persist for a long time after all traces of the para- 

 site have disappeared — become, in fact, constitutional, where the 

 temperament or diathesis, such as herpatism, is allied witli 

 it. The disease may then be designated chronic lichen, and de- 

 mands different treatment. — (Fleming.) 



The course of the disease is slow in horses well fed and cared 

 for ; but in those under less favourable circumstances it spreads 

 with great rapidity, and may even cause death from irritation and 

 exhaustion. Mr, Fleming, who has seen the disease in the Crimea, 

 says : — " It has been remarked that after the disease had been 

 cured, the hair on the affected parts grows very rapidly, and 

 longer than elsewhere ; and also that it is darker coloured, as if 

 the poison of the sarcoptes had exercised a specific influence on 

 the hair bulbs." 



Si/jnjjtoms of Dcrinatodedic Scabies. — This is the variety of 

 mange usually recognised in this country ; indeed, I am not 

 aware of having seen the sarcoptic form, except during an out- 

 break which occurred in 1872-73, and which was conveyed from 

 Edinburgh to Melrose, proving fatal to several horses. It is 

 characterised by great itchiness, associated with the formation 

 of papules and pustules. The papules are distinct elevations 

 about an eighth of an inch in height, and a third of an inch in 

 diameter, soon having upon their surface a vesicle, that is quickly 

 ruptured, allowing the serous contents to escape : these serous 

 contents dry and form a crust. The pimples continue to dis- 

 charge, and the crust increases and continues moist, giving an 

 appearance different to the dry powdery sarcoptic crust. 



These parasites invade the upper border of the neck and root 

 of the tail ; they deposit a secretion more acrid and irritating, and, 

 having long mandibles, they thus cause more serious alteration 

 in the skin than the sarcoptic ; but notwithstanding, this form 

 of scabies is not so serious, is less contagious, spreads more 

 slowly, and is more easily cured than the other form. 



Si/mptoms of Symbiotic Scabies. — These parasites, like the der- 

 matodectic, live in colonies, and thus differ from the sarcoptic, 

 which lead an isolated existence. They invade the limbs of 

 horses, and do not burrow into, but merely bite the skin, causing 

 the production of serum, which, along with the debris of the epi- 

 dermis, concretes into numerous crusts that break in large flakes. 



