140 HEALTH AND DISEASE 



fact that skin diseases, with a few exceptions, are not fetah Those afiec- 

 tions which are hereditary are the most difficult to cure. Psoriasis, eczema; 

 and urticaria, and, it may be added, those forms of itching which are 

 not associated with any eruption, such as pruritus, are likely to recur, 

 although they may yield to simple treatment. 



In the case of parasitic disease, such as ringworm and mange, in the 

 horse, the cure is generally tolerably easy if taken in the early stages; 

 in cases where the animal has been long neglected, especially when the 

 disease is due to the burrowing mite (sarcoptic mange), the cure some- 

 times proves to be absolutely impossible, and in many of these cases 

 the system has become so debilitated by the ravages of the parasite and 

 the unrest of the patient that a fatal result is by no means uncommon. 

 More frequently still it is considered advisable to destroy the subject as 

 incurable. 



THE PRINCIPLES OF TREATMENT 



Reference to the causes which have been indicated will at once suggest 

 that the remedies required may be purely local, or constitutional, or a 

 combination of the two. In the case of purely local afiections, such as 

 the irritation excited by irritants, erythema, simple eczema, and parasitic 

 diseases, local applications will usually suffice, although even in such cases 

 it will have to be borne in mind that the state of the system will mate- 

 rially influence the progress of the disease, and certain changes of diet, 

 or regulations as to exercise and work, may be expedient, if not absolutely 

 necessary. All forms of skin disease which come under the head of acute 

 specific disorders — variola, horse-pox, urticaria from indigestion, medicinal 

 rashes, lead poisoning, nerve diseases, and others of a like kind — will be 

 dealt with by constitutional means ; the employment of local remedies will 

 be admissible as palliatives, as, for example, where the itching from medi- 

 cinal rashes, neurotic diseases, sympathetic pruritus, or urticaria ab 

 ingestis renders the animal restless and sometimes prevents it from taking 

 its food. 



ERUPTIONS OF THE ACUTE SPECIFIC DISEASES 



Variola Equina or Horse-Pox. — It is a matter of history that at 

 one time it was an accepted doctrine, in regard to the origin of vaccine 

 matter, that the disease in the cow which was described as cow-pox was 

 the result of infection from a disease in the horse which attacks the heels 

 of the animal and is named " grease ". 



According to Professor E. M. Crookshank, in his classical work on the 

 pathology of vaccination, the disease was thus described by Jenner: 



