ARTHROPODA 557 



layer from whicli the acarus is extracted ; decided itching immediately arises, 

 perhaps in consequence of the discharge of an irritating fluid. Boring its way 

 transversely from without inward to deposit its eggs, the acarus makes a pas- 

 sage parallel with the first to the surface of the skin. Prom the eggs, about 

 50 in number, deposited in this passage an embryo develops, which after from 

 four to seven days makes its ovm opening to the external skin. After a short 

 time it again bores its way into the skin to pass through a desquamation proc- 

 ess, which is repeated several times, and about fourteen days later it appears 

 as a mature insect upon the skin. The male does not bore its own opening, 

 but only hollows out a funnel-like groove in which it lives. 



The transmission of the acarus from man to man occurs occasionally by 

 means of clothing, but, as a rule, by intimate contact with the diseased skin, 

 and in almost every case by sleeping with a scabies patient. Among the 

 poorer classes, therefore, a scabies patient is likely soon to infect the entire 

 family. The disease is often spread by prostitutes. 



The acarus is apt to attack the flexor surfaces of the joints of the hand 

 and fingers, the interdigital folds, the lateral surfaces of the fingers ; in chil- 

 dren with a delicate skin the palm of the hand, the surroundings of the elbow- 

 joint, the anterior axillary fold; and in women the nipple. The navel, the 

 skin of the penis and scrotum, the trochanter region, the flexor of the knee 

 and the internal border of the foot are attacked. The acarus also prefers all 

 those portions of the body upon which the underclothing is tight. The face 

 and hairy scalp are rarely attacked. Samisch has described a case in which 

 scabies gave rise to severe inflammation of the eyes ("keratitis," "Biischel- 

 form"). 



The irritation from the itching which the parasite produces by its burrow- 

 ing in the skin is very acute, especially at night, for at this time, stimulated 

 by the warmth of the bed, the mite nourishes itself. The affected individual 

 attempts to relieve the irritation by vigorous scratching. Not only are the 

 small nodular efflorescences produced by the parasites irritated by this scratch- 

 ing, but, in addition, new papular elevations are formed at the exit of the hair 

 follicles, and small vesicles like millet seeds with purulent contents. Contin- 

 ued scratching causes new eruptions, while the older ones are torn away, and 

 become covered with striae-like blood crusts, from which finally ulcers covered 

 with eschars develop. Marked pustular eruptions often follow even in young 

 people and eczema develops in all those who suffer for a long time from the 

 disease. The diagnosis of scabies may readily be made from the localiza- 

 tion of the excoriations, as eczema upon the nipple, upon the fold of the axilla, 

 upon the penis, etc. 



A peculiar picture resembling the mange of animals is produced by scabies 

 norvegica s. crustosa. This shows a thick, dirty-gray induration composed of 

 deposits of epidermis upon the palm of the hand, on the sole of the foot, on 

 the elbows, on the face and the hairy scalp. These indurations contain the 

 parasites and their ova often in enormous numbers. According to Fiirsten- 

 berg this form of scabies is due to the smaller sarcoptes scabiei crustosa, 

 Fiirstenberg. 



The disease usually develops typically in one and a half to three months 



