But even those contagious diseases that are caused by skin germs or animalcules will not be wholly cured by any applications whatever. Constitutional remedies should go hand in hand with these. And, indeed, so great is the defensive power of strong, pure blood, rich in its white corpuscles or leucocytes, that I believe I could cure even the worst forms of mange by internal remedies, good food, and tonics, etc., without the aid of any dressing whatever except pure cold water. In treating of skin diseases it is usual to divide them into three sections: (1) The non-contagious, (2) the contagious, and (3) ailments caused by external parasites. (1) The Non-Contagious.--(a) Erythema.--This is a redness, with slight inflammation of the skin, the deeper tissues underneath not being involved. _Examples_--That seen between the wrinkles of well-bred Pugs, Mastiffs, or Bulldogs, or inside the thighs of Greyhounds, etc. If the skin breaks there may be discharges of pus, and if the case is not cured the skin may thicken and crack, and the dog make matters worse with his tongue. _Treatment_--Review and correct the methods of feeding. A dog should be neither too gross nor too lean. Exercise, perfect cleanliness, the early morning sluice-down with cold water, and a quassia tonic. He may need a laxative as well. _Locally_--Dusting with oxide of zinc or the violet powder of the nurseries, a lotion of lead, or arnica. Fomentation, followed by cold water, and, when dry, dusting as above. A weak solution of boracic acid (any chemist) will sometimes do good. (b) Prurigo.--Itching all over, with or without scurf. Sometimes thickening. _Treatment_--Regulation of diet, green vegetables, fruit if he will take it, brushing and grooming, but never roughly. Try for worms and for fleas. (c) Eczema.--The name is not a happy one as applied to the usual itching skin disease of dogs. Eczema proper is an eruption in which the formed matter dries off into scales or scabs, and dog eczema, so-called, is as often as not a species of lichen. Then, of course, it is often accompanied with vermin, nearly always with dirt, and it is irritated out of all character by the biting and scratching of the dog himself. _Treatment_--Must be both constitutional and local. Attend to the organs of digestion. Give a moderate dose of opening medicine, to clear away offending matter. This simple aperient may be repeated occasionally, say once a week, and if diarrhoea be present it may be checked by the addition of a little morphia or dilute sulphuric acid. Cream of tartar with sulphur is an excellent derivative, being both diuretic and diaphoretic, but it must not be given in doses large enough to purge. At the same time we may give thrice daily a tonic pill like the following:-- Sulphate of quinine, 1/8 to 3 grains; sulphate of iron, 1/2 grain to 5 grains; extract of hyoscyamus, 1/8 to 3 grains; extract of taraxacum and glycerine enough to make a pill.