784 ANIMAL PARASITIC SKIN DISEASES. 



of the sarcoptic acarm, which closely resembles the itch insect 

 of man, is rather less common than the other form affecting 

 the general sm-face of the body, the effect of the residence there 

 of tiie Dermatodectes equi. In both forms the earliest indica- 

 tions of the parasite's existence are itching and irritability of the 

 skin ; this in the dermatodectic or i:)soroptic variety, when 

 fairly established, being rather more pronounced, and the 

 damage done to the tissues through rubbing is usually greater. 

 The initial and elementary lesions of sarcoiJtic mange in the 

 horse, are said to be vesicular, as those of the 'psoroptic are 

 papular, or papulo-vesicular. 



These differences are, however, in many instances rather 

 difficult accurately to determine. 



In the former, there is a more uniform distribution of the 

 skin irritation, and a greater disposition to simulate non- 

 parasitic eczema, by the large and general distribution of small 

 elevations of dried serosity. In the latter variety, the papules 

 which exude the serous Huid do not immediately dry up, but 

 continue weeping, and thus render the superincumbent crust 

 more extensive and rather moist ; the scabs are consequently 

 larger and less dry than in the sareoptic variety. 



The rapidity of the extension of these two varieties in the 

 individual animal, and their powers of propagation, are not 

 exactly alike. The more common form, the psoroptic, is slower 

 in the distribution of the acari over the affected animals, 

 being disposed to continue for variable periods as distinct ch- 

 cumscribed patches, and is less commonly found propagating 

 amongst a number of horses which may have had a certain 

 amount of communication with each other. It is also more 

 disposed to be located close to, or in connection with, the per- 

 manent hairs of the mane and tail, than the other, Avhich is 

 the result of the activities of the burrowing acavi 



The symhlotlc scabies, like the other forms more parti- 

 cularly affecting the body, owes its existence to the activities 

 of the acari known as the Cliorioptes vel Symhiotes equi. 

 The mites here are so far like the Dermatodectes, that the}' 

 do not burrow beneath the epidermis or crusts, but live 

 amongst them; and they are particularly tenacious of resi- 

 dence in the localities embraced in the limbs. It is a disease 

 particularly of coarse -bred and hairy-limbed horses, and is 



