680 DISEASES OF THE SKIN". 



healthy, and it is essentially a chronic and often an intract- 

 able disease; but it never spreads over any great extent of 

 surface, being generally confined to the flexures of the limbs. 



I have reason to think that, like lymphangitis, grease, and 

 anasarcous swellings of the legs, it is often of hereditary origin. 



The scaly eruptions of psoriasis are unsightly, lower the value 

 of an animal, and are occasionally troublesome, crack, inflame, 

 and discharge a bloody serosity. 



Treatment. — Generally remedies seem to have no effect, and 

 beyond modifying the condition of the cracks when inflamed, 

 the efforts of the practitioner are productive of no positive 

 results. 



To prevent the formation of the cracks and chasms, the scales 

 should be dressed occasionally with some oily material; and 

 when they become much thickened by accumulation, they are to 

 be well soaked in an alkaline solution, carefully washed off, and 

 the raw skin, thus exposed, touched with the nitrate of silver. 

 An occasional application of the unguentum hydrargjTum is also 

 useful. 



In the case of a valuable animal, where the eradication of the 

 disease is a question of importance, the treatment must be both 

 local and general. 



The general treatment comprises a purgative, followed by 

 arsenic and cantharides, either separately or in combination — 

 the iodide of arsenic, or by a triple compound of arsenic, iodine, 

 and mercury, which may also with advantage be employed as a 

 local remedy ; it is made as follows : — 



B^ Liquor hydriodatis arsenici et hydrargyri : triturate of finely 

 levigated metallic arsenic, 6'08 grains ; mercury, 15"38 grains ; 

 and iodine, 50 grains, with 1 drachm of alcohol, until the mass 

 be dry, and changed in its colour from a deep brown to a pale 

 red. Next triturate the mass for a few moments with eicjht 

 ounces of distilled water ; transfer the solution to a bottle, add 

 to it haK a drachm of hydriodic acid, and filter, making up to 

 eight ounces by means of distilled water if there is any defi- 

 ciency. The solution is of a golden yellow colour, and each 

 drachm contains — water, 1 drachm ; protoxide of arsenic, i 

 grain ; protoxide of mercury, ^ grain ; iodine converted into 

 hydriodic acid, ^ grain. The dose of this for the horse is from 

 two to three ounces twice a day, care being taken that its effects 



