704 SCABIES. 



rind towards the front, lohg stiff hairs. The females, which 

 nre far more abundant, only differ from the males in 

 their size, being about one- third longer, and in the struc- 

 ture of the two posterior pairs of feet, which are attached 

 to the belljr, close together, of equal length and strength, but 

 shorter and weaker than in the male. The external (third) 

 jiair of feet has two long terminal hairs, but no sucking disc. 

 The internal (fourth) pair has the rudiments of a claw, a sucking 

 disc, ojid a fine terminal hair at the base of tlie stalk of the 

 tmcking disc The colour of the parasite is whitish ; tlie horny 

 •Iceleton reilJish-brown — ferruginous. The eggs are very large, 

 <ioa*'ed witli a sticky mass, and are often carried about by the 

 ^emnJe between her legs. The eggs are deposited in small 

 ij all cries under the epidermis. The young are very small, but 

 grow very q^uickly during the first four days ; and, according to 

 ifertwipf, have their eight feet at once, but only six according 

 fo Ilering. Their movements are effected q^uickly, and by 

 means of the feet provided with sucking discs. They may be 

 kept alive for three weeks without nourishment. Wherever 

 they penetrate the skin, a small knotted elevation is produced, 

 •rith a small pa'="sage, at the extremity of which the acarus sits. 

 Ihe epidermis becomes soft, separates from the true skin, and 

 .uv exudate is thro^\n out, which, along with the epidermis, 

 iliico into scaly scurfs, that become detached. 



The tiansference of this acarus from the horse to man has 

 been proved by many observers — for example, E. A^'iborg, Sydow, 

 Osiander, Greve, Groguier, and Hertwig — as well aa the trans- 

 ference of the disease so caused from one man to another ; 

 but the mites do not propagate on the human skin, and the 

 symptoms of their presence spontaneously disappear about the 

 twelfth day. 



The sarcoptes equi is transmissible to horned cattle ; but it 

 13 as yet doubtful if the dog, cat, and pig are susceptible of 

 the mange induced by it Gerlach failed to communicate the 

 disorder to the sheep, although the mites were by him placed 

 on the skin. 



TirE DERMATODECTES EQUL 

 The dermatodectes equi, which has hitherto been looked 

 upon S3 the veritable sarcoptes or acarus equi, does not live, 



2 V 



