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DISEASES OF THE SKIK 



1. Sarcoptes. 



2. Psoroptes (Gervais), Dermatodeetes (Gerlach), Dermatokoptes 

 (Fiirstenberg). 



3. Symbiotes (Gerlach), Chorioptes (Gervais), Dermatophagus 

 (Fiirstenberg). 



A. The Sarcoptes dig sub-epidermic galleries and live on the 

 plasma cells of the Malpighian layer ; they multiply in these gal- 

 leries and occasion a very intense dermatitis. They are character- 

 ized by their general form, which is that of a shield, and by their 

 small size (0.2 to 0.5 millimetre) ; they can only be seen by means 

 of a microscope. The head, which is horseshoe- shaped, is fitted 

 with two strongly developed conical mandibles ; the legs are short, 

 stumpy; the suction cups, which are tulip-shaped, exist in the males 

 on the first, second, and third pair of legs ; in the females on the 

 first two pairs only. 



Authors disagree on the subject of the varieties in the sarcoptes ; 

 Fiirstenberg has attempted a division based upon morphological 

 characters ; Gerlach has advised a biological grouping ; but the in- 

 consistency of these varieties and their exaggerated number has 

 been well pointed out (Zurn, Johne). We have adopted the divi- 

 sion established by Siedamgrotzky, who recognizes two principal 

 groups : 



a. The large sarcoptes, comprising : 



(1) Sarcoptes scabiei of man, horse, and lion. 



(2) Sarcoptes squamiferus of the dog, pig, sheep, and goat. 



b. The small sarcoptes {Sarcoptes minor), which is found in the 

 cat and rabbit. 



B. The Psoroptes live upon the surface of the skin ; adhere to 

 the fatty matter and the hair ; suck the blood and lymph of the 

 integument by means of their buccal organs, producing a more or 

 less intense dermatitis, through the numerous stings which they 

 inflict. They are characterized by their relatively great size (0.5 

 to 0.8 millimetre), which allows them to be seen with the naked eye 

 upon dark surfaces ; they are very easily seen with the help of a 

 magnifying glass. The head is elongated and pointed; the man- 

 dibles are long, straight, and stinging ; the legs are very long ; the 

 sucking cups, tulip or trumpet shaped, are carried by articulated 

 pedicles. In the male they are seen upon four pairs of legs ; in 

 the female, upon the first, second, and fourth pairs only. Ziirn 

 divides these as follows : 



