It may be stated at the outset that the horse is comparatively exempt from many of the diseases referred to in the systems of classification which have been quoted; but in making this admission it is important to note that the skin diseases of the horse did not attract any particular attention from the older veterinary writers, and even in regard to the authorities of the present time, although they have adopted a system of classification taken with certain modifications from the system accepted by the most distinguished dermatologists, nothing like a special course of study of the skin diseases affecting the lower animals has yet been initiated in our schools. It seems to be even now taken for granted that in its veterinary aspect dermatology need not be elevated to the prominent position which it occupies in medical science as applied to the human subject. It will not, however, be out of place to suggest that a closer study of the methods of diagnosis, prognosis, and principles of treatment, might lead to considerable changes in the above views.
To arrive at a correct conclusion as to the nature of any form of skin disease, the examiner must be armed with practical knowledge of the various types in which eruptive affections are exhibited, the course which the particular eruption follows, and its probable termination; and particularly is it essential that he should know whether the affection is acute or chronic, and whether it is of a kind which comes under the heading of periodicity, and whether it is associated with any form of specific fever.
In cases of diseases of the skin which are not attended at the time of the examination with any kind of eruption, the general condition of the animal and any change in the colour of the skin have to be noted, in order that an opinion may be formed as to the probability of an eruption appearing as the disease advances. In short, it is most important to determine by critical examination the exact nature of what are called by pathologists elementary lesions, all of which are distinguished by certain terms. For example, when the skin is discoloured by some alteration in the quantity or arrangement in the colouring material as the result of the irritating action of parasites, or by chemical agents, the term maculoe. is applied to the discoloured patches. Stains which are due to the escape of blood from the vessels of the skin are designated purpura, and are therefore excluded from the designation maculae.
Erythema means a redness of the skin arising from a determination of blood to a part. The appearance itself is easily recognized, but taken alone it does not indicate the particular disease out of which it arises, as it may depend upon a variety of causes.