136 PARASITIC SKIN DISEASES. 



gallery is marked on the skin hy a red line, which, somewhat re- 

 sembles the scratch of a pin ; but it is not visible in the skin of a 

 horse, owing to the thickness of the soarf-skin of that animal. If 

 a pin be pushed into the gallery, the parasite can be removed at 

 the point of the pin. The male parasites (which form only about 

 a twentieth of the entire number), the unimpregnated females, and 

 the larvae reside among the crusts on the skin. Although the 

 disease may be fully established on some portions of the skin, which 

 will consequently become thickened, thrown into folds, and bald ; it 

 may be in its first stages on other parts, upon which the grain-like 

 eminences made by the newly-formed crusts, can be felt among 

 the hairs of the coat. The disease takes from one to two months 

 to become fully established. Rubbing the affected surface, and 

 manifestation of pleasure when the mangy spots are scratched with 

 the fingers, are prominent features of the complaint. 



3. The insects of the third form of mange are called symhiotes. 

 Their invasions are confined practically to the legs, and extend 

 very slowly from one part to another. They commence their attack 

 at the back of the pastern, and work upwards ; but rarely go higher 

 than the knee and hock, and are seldom found except on coarse, 

 hairy-legged animals. They affect the hind limbs oftener than the 

 fore, and those of young horses more frequently than those of old 

 ones. Strange to say, they manifest their presence as a rule only 

 during winter ; the probable reason of this being, as explained by 

 Neumann, that the excretions from the skin during the summer 

 are sufficient for their nourishment. Possibly for a similar reason, 

 namely, that the skin is more active during work than during 

 repose, the horse suffers more from their attentions at the latter 

 time, than at the former. The symptoms are : itching ; the for- 

 mation of crusts, cracks, and sores ; thickening of the skin ; and 

 falling-out of the hair. When the pasterns are affected, the symp- 

 toms may resemble those of grease or grapes (p. 156). " At the 

 commencement of the attack, the only important symptom whicji 

 attracts attention, is the habit which the mangy horse has when 

 he is at rest, of abruptly striking the ground with a hind foot for 

 hours at intervals and especially during the night. Some horses 

 kick. All scratch and bite the fetlocks " [Friedherger and 

 Frohner). 



ERUPTION. — The nature of the eruption is due to the venomous 

 bites of the insects and to friction in the efforts made by the suf- 

 fering animal to relieve itself from the itching by scratching or 

 rubbing itself. 



ITCHING. — The itching appears to be caused by the irritating 

 saliva which these insects deposit on the wounds they make in 



