54 ANIMAL PARASITES. 



(fourth) pair has the rudiments of a claw, a sucking disc, and a 

 fine terminal hair at the base of the stalk of the sucking disc. 

 The hairs and tubercles at the anus are smaller and more rare. 

 The generative organs are not exactly known. 



The colour of the animal is wjritish ; the horny skeleton red- 

 dish-brown, ferruginous. The eggs are very large, coated with a 

 sticky mass, and are often carried about by the female between 

 her legs. The eggs are deposited in small galleries under the 

 epidermis. The young are very small, but grow very quickly 

 during the first four days ; and, according to Hertwig, they have 

 their eight feet at once, but only six according to Hering, so 

 that they also undergo a change of skin. Their movements 

 are effected quickly, and by means of the feet provided with 

 sucking discs. They may be kept alive for three weeks without 

 nourishment. Wherever they penetrate into the skin, a small, knot- 

 like elevation is produced, with a small passage, at the extremity 

 of which the mite sits. The epidermis becomes soft, separates 

 by exudation from the cutis, and dries, in animals, into scaly 

 scurfs, which become detached. All these mites produce, in ani- 

 mals, similar phenomena to those presented by the Norwegian 

 prurigo in the human subject. 



The transference of the mite to man has been proved by 

 many observers, as, for example, E. Viborg, Sick, Sydow, Osian- 

 der, Greve, Groguier, and repeatedly by Hertwig, under whose 

 inspection Schade made the experiment of inoculating himself 

 with this mite, by placing the mites upon his arm and covering 

 them with fine paper, the edges of which were fastened down 

 with court plaister. In five minutes, itching was produced, which 

 increased and diminished periodically for five days ; in thirty -two 

 hours the skin exhibited several raised red points of the size of 

 a pin's head, and near these small passages under the epidermis, 

 which became gradually more distinctly marked up to the fifth 

 day, and exhibited small vesicles with a clear fluid. On the 

 twelfth day the itching had disappeared, and everything dried up 

 into scabs, beneath which there was a healthy epidermis. Whe- 

 ther Greve' s observations of the residence of the same individual 

 mites upon the human skin for three, six, and eight weeks before 

 healing took place, be an error in the above-mentioned sense, I 

 am unable to decide. Greve and Hertwig also saw the transfer 

 of the disease from one man to another, notwithstanding that the 

 mites do not propagate upon the human body. 



