776 DISEASES OF ACCESSORY ORGANS AND STRUCTURES. 



all cases, or nearly all in my experience, affected animals of 

 adult life, and which were in full work. I have not in them 

 observed that they have been the subjects of any particular 

 dispase, or that any marked constitutional disturbance attended 

 this cutaneous affection. They have, however, all been horses 

 subject to sudden spurts of fast work, entailing general vascular 

 excitement, followed by sudden and ill-regulated periods of 

 rest. When occurring, it has only affected the deciduous hairs, 

 not those of the tail or mane ; and the removal of these has 

 in every case been accomplished with little or no alteration in 

 the pigmentation. 



Symptoms, etc. — It is usually sudden in its development, 

 with little or no cutaneous irritation, itching, appearance of 

 exudation, or even raising of the epidermis. 



It is first observed over the back, sides, and neck, where the 

 hair, in the ordinary process of grooming the animal, is de- 

 tached without the slightest evidence of pain, leaving perfectly 

 smooth and bald patches of varying form and size. With 

 many, the greater part of the entire hairy covering may be 

 detached in flakes or patches, which, when removed, are held 

 together in separate portions by the removal in a planiform 

 manner of the upper layer of the epidermic cells. When the 

 hair has been detached, there is no itching nor perverted sensa- 

 tion of the exposed skin, which is perfectly smooth, soft, and 

 unctuous, having a very light covering of scales. 



Pathology. ^ — It is extremely difficult, or rather impossible, to 

 account in a clear and definite manner for this sudden and 

 often extensive change. All that we are really able to say is, 

 that it appears as the immediate result of disturbed nutrition 

 and atrophic changes of the epidermis and hair-follicles. 



The existence of a vegetable parasite in connection with the 

 hairs or the follicles, as in the different forms of Tinea, has 

 been put forth as the active agent in the death of the hair ; 

 this, however, does not seem the true solution of the question. 

 When such organisms have been observed, they are probably an 

 accidental occurrence. The most extensive and destructive ex- 

 hibitions of alojoecia which I have encountered have certainly 

 been unconnected with parasitic existences. 



Although it is a mistake probably to lay too much stress on 

 the actual appearance and state of the individual hairs, still 



