GENERAL PART OF EXAMINATION. 



55 



d. Sarcoptic mange. Seen in the horse, dog, swine and cat, 

 etc. This mite burrows tunnels in the epidermis, causes nodules, 

 crust formation, thickening and folding of the skin, pruritis. Most 

 difficult mite to capture for microscopical examination; to obtain 

 material for examination the skin should be scraped to bleeding. 

 Sarcoptes are very small, turtle-shaped mites measuring 0.2 — 0.5 mm 

 head horse-shoe shaped, legs short and stumpy. 



e. Acarus mange. Most common in dogs and swine, ap- 

 pearing principally on the eyelids, head, extremities, causing 

 little itching. Skin covered with scales, small pustules, and is 

 thickened and folded. In the squamous form circumscribed, bald, 

 bluish-red areas occur, epidermis mother-of-pearl-like, scaly. The 

 parasite is vermiform, 0.2 — 0.3 mm with a long, narrow, jointed 

 body, the anterior portion carrying four pairs of short, three- 

 jointed feet, at the end of each, three pointed hooks. Eggs spindle- 

 shaped. 



III. Skin Diseases Due to Plant Parasites. 



Ringworm (Herpes tonsurans) is induced by the fungus Tri- 

 chopyton tonsurans. The disease is characterized by the appear- 

 ance of small round, well-defined hairless patches. The smooth 

 skin is covered with grey-colored, asbes- 

 tos-like crusts. Spontaneous healing begins 

 in the center of the lesion, extending 

 toward the periphery ("ringworm"). Vesi- 

 cles rarely appear. Most common in the 

 ox. In the crusts and more especially in 

 the hair follicles great numbers of round 

 or ovoid, light-refracting spores can be 

 seen with the aid of the microscope. The 

 spores measure 4u. Some of the spores are 

 arranged in regular order, like a string of 

 beads, others are disposed in irregular 

 groups. The filaments, which may be sim- 

 ple or jointed, show little tendency to 

 branching; their free ends are rounded. 



Favus. Rare, but appears in fowls as 

 so-called "white comb" (Tinea galli). 

 Small whitish-grey spots come upon the 

 comb, which gradually is encrusted by 

 them. In mammals thick, depressed, yel- 

 lowish brown crusts appear. 



Fig. 14. 



Trichophyton tonsurans. 



