DISEASES OF THE SKIN 139 



9. Climateric or endemic iiitiueuces, often malarial in nature, which act 

 by deteriorating the system generally. 



10. Disorders of the liver and spleen, leading to pigmentary deposit in 

 various parts, jaundice and pruritus, &c. 



This extract has been modified by the omission of certain diseases which 

 are not recognized in the horse. All the morbid conditions above referred 

 to relate to changes produced in the blood generally by the introduction 

 of poisonous substances, or by the accumulation of animal poisons, or 

 from the failure of the excretory organs to carry them out of the system. 

 There are, however, in addition, to be considered various forms of mal- 

 nutrition which lead to changes in the tissues of the skin. Changes are 

 also produced by local irritants, as chemical agents, burns, and the ravages 

 of parasites. It must be allowed, also, that there are certain conditions 

 of the skin, due to heredity, which dispose the surface to certain forms of 

 disease, such as psoriasis, cancer, and ichthyosis. Further, there are causes 

 which act specially upon the nerves, as frequent contact with local irritants, 

 changes of temperature. The action of local irritants, it may be observed, 

 is frequently connected with occupation, illustrated in the case of horses 

 which are working where building is being carried on, which exposes them 

 to frequent contact with lime, either dry or moist, or in the case of hunters 

 which are commonly used in districts where the soil contains some gritty 

 or irritating particles which act upon the surface, giving rise to what is 

 known as " mud fever ", a disease which is traceable also to the habit of 

 washing the extremities and other parts of the body with warm water after 

 work. 



To sum up the causes of skin diseases: — 1. Clianges in tlie blood 

 induced by poisons, dietetic errors, tuberculous disease, rheumatic ten- 

 dency, general debility, effects of malaria. 2. Clianges in the tissues, 

 due to mal-nutrition, local irritation, whether from chemical or physical 

 agencies, inherited peculiarities of the tissues. 3. Influences which act 

 specially on the nerves, as dirt, exposure to excessive cold or heat, and 

 sometimes organic disease of certain organs which by sympathy excite 

 chronic congestion of different parts of the skin. 



PROGNOSIS 



Having considered the possible or probable causes, the next step will 

 be to decide as to the duration of the disease, and the chances or otherwise 

 of cure — matters in which the owner of the horse is always particularly 

 interested. Prognosis will be materially assisted by a history of the case. 

 In the first place, the ground may be cleared by the recognition of the 



