CRACKED HEELS. 443 



losis in the lung. The worm or its debris is found in the center of 

 such masses. These sores are very obstinate, resisting treatment for 

 months in summer, and even after apparent recovery during the 

 cold season they may appear anew the following summer. In bad 

 cases the rubbing and biting may cause exposure of synovial sacs and 

 tendons, and cause irremediable injury. Even in winter, however, 

 when the diseased process seems arrested, there remain the hard, 

 firm, resistant patches of the skin with points in which the diseased 

 jjroduct has become softened like cheese. 



The apparent subsidence of the disease in winter is attributed to the 

 coldness and comparative bloodlessness of the skin, whereas in sum- 

 mer, with high temperature, active circulation, and rapid cell growth, 

 inflammation is increased, itching follows, and from the animal rub- 

 bing the i^art the irritation is persistently increased. The hotter the 

 climate the more troublesome the disease. 



The life history of the parasite is unknown, but it probably enters 

 the system with the food or water. 



Treatment consists, first, in placing the animal in a cool place and 

 showering the surface with cold water. The parasite may be de- 

 stroyed by rubbing the surface of the wound with iodoform and 

 covering it with a layer of collodion, and repeating the applications 

 every twenty- four hours for fifteen days, or until the sores heal up. 

 Ether or chloroform may be used in place of iodoform, being poured 

 on cotton wool and applied to the sore for two minutes before paint- 

 ing it with collodion. 



CRACKED HEELS (SCRATCHES, OR CHAPS ON KNEE AND HOCk). 



This usually sets in with swelling, heat, and tenderness of the hol- 

 low of the heel, with erections of the hairs and redness (in white 

 skins), with stiffness and lameness, which may be extreme in irritable 

 horses. Soon slight cracks appear transversely, and may gain in 

 depth and width, and may even suppurate. More frequently they 

 become covered at the edges or throughout by firm incrustations re- 

 sulting from the drying of the liquids thrown out, and the skin be- 

 comes increasingly thick and rigid. A similar condition occurs 

 behind the knee and in front of the hock (malanders and salanders), 

 and may extend from these points to the hoof, virtually incasing that 

 side of the limb in a permanent incrusting sheath. 



Causes. — Besides a heavy lymphatic constitution, which predisposes 

 to this affection, the causes are overfeeding on grain, unAvholesome 

 fodder, close, hot, dirty stables, constant contact with dung and urine 

 and their emanations, working in deep, irritant mud; above all, in 

 limestone districts, irritation by dry limestone or sandy dust in dry 

 weather on dirt roads; also cold drafts, snow and freezing mud, 

 washing the legs with caustic soap, wrapping the wet legs in thick 



