136 HEALTH AND DISEASE 



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. 



DIAGNOSIS 



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 par- 

 ticularly 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 macula: 

 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. 



Wheals. This term is used to indicate certain elevations of the 

 surface of the skin, the centre of which presents a pale colour, having 

 the appearance produced by the sting of the nettle. Wheals are caused by 

 sudden dilatation of the blood-vessels, followed by the escape of fluid from 

 them into the centre of the swelling. These appearances, however, are not 

 generally recognizable in the horse, owing to the colour of the skin and the 

 covering of hair. 



