686 DISEASES OF THE SKIN". 



Mr. Gamgee, translating from Gerlacli, gives the following 

 arrangement of the species belonging to each genus : — 



A* Sarcoptes. B. Dermatodectes. O. Symhiotes. 



1. S. hominis. 1. D. equi. 1. S. equi 



2. S. equi 2. D. bovis. 2. S. bovis. 



3. S. suis. 3. D. ovis. 3. S. elephantis. 



4. S. cards. 



5. S. catis. 



6. S. caniculi. 



To the genus sarcoptes belong also : — 



S. rupicaprae. — (Hering.) 

 S. dromedarii. — (Gervais.) 



The experiments of Hering, Hertwig, and others have proved 

 that the mange insect may be transferred from the lower animals 

 to man ; that they bore the human skin, erect galleries in it, 

 and cause itch-like eruptions. In general, however, the erup- 

 tions last only as long as the individual life of the mites trans- 

 ferred. Upon this point observations vary, some extending the 

 continuance of the eruption to a period of six weeks, whilst 

 others limit it to two or three. All are, however, agreed that 

 they do not procreate in the human skin ; that, although those 

 in attendance on mangy horses may suffer from the disease, they 

 do so only very slightly, and but for a limited period. 



SAECOPTES HOMINIS (ACARUS SCABIE). 



" The male is about one-third smaller than the female. He 

 has suckers on two hind feet, and possesses on the abdominal 

 surface genital organs, all of which characters are absent in the 

 female. She, on the other hand, in addition to her size, and the 

 negative marks alluded to, is characterised by three kinds of 

 horny spines, which are scattered over her back. The suckers, 

 or ambulacria, are organs of locomotion ; the mandibles enable 

 it to cut the epidermis, and extract fluid from the tissues, which 

 passes through a delicate oesophagus, the termination of which 

 is undermined; the body of the animal being filled with an 

 unorganized, very fine molecular pulp. A short, delicate tube 

 may also sometimes be observed at the anus — a supposed 

 rectum. Ko respiratory apparatus can be discovered, although 



