Etiology. 969 



In the domestic animals the following hair follicle mites occur : 



1. Demodex follieulorum (var. canis) ; the head and chest part somewhat 

 shorter than the abdomen; the male 0.22 to 0.25 mm., the female 0.25 to 0.30 mm. 

 long; both 0.045 mm. wide; the eggs spindle-shaped 70 to 90 microns long, 25 

 microns wide. Originator of acariasis in the dog. 



2. Demodex phylloides; comparatively broad, laurel-leaf like, the length 

 of the head and chest part and of the post-abdomen about equal; the male 0.22 mm. 

 long, 0.057 mm. broad, the female 0.25 to 0.26 mm. long, 0.06 mm. wide; the eggs 

 oval, constricted at each end (Csokor). Cause of acariasis in the pig. 



Besides these one encounters special varieties of mites in the seba- 

 ceous glands of the other animals. 



Of the tenacity of hair sac mites the following may be stated from the 

 investigations of Brandl & Gmeiner and those of Gmeiner: — In dry air the mites 

 are capable of living ly^ days at most, while in very moist atmosphere they remain 

 alive as long as three days, but they are killed in a few seconds by a temperature 

 of over 41°. They resist the cold of winter for three days at most if the 

 humidity is high. 



Of chemical substances the hair follicle mites are killed immediately by acid, 

 carbol. liquefactum, bacillol, creolin, cresolum crudum, creosote, liquor cresoli 

 saponatus, lysol, tar, chloroform, bisulphide of carbon; in about a minute by the 

 ethereal oils, especially ol. anethi and ol. carvi, further aqua cresolica, creolin, 

 cresol or tar liniment, 2 to 10% carbolic acid solution; in 2 minutes by tincture 

 of iodine, formaldehyde-solution; in 3 minutes by salicylic acid in 10% alcohol, 

 and 1% alcohol eudermol solution; in 6 minutes by Gmeiner 's solution of ol. 

 carvi with alcohol and castor oil. The mites were killed by Peruvian balsam (pure) , 

 in 12, by liquid styrax in 55 and by 1% corrosive sublimate solution in 19 minutes. 



The infection occurs undoubtedly in the great majority of 

 cases by immediate contact of healthy with diseased animals. 

 Short-haired and young dogs are especially susceptible (among 

 177 dogs observed by Schindelka to be suffering from acariasis, 

 141 were short-haired, and only 36 long-haired), which is ac- 

 counted for by the fact that in short-haired dogs the mites gain 

 access to the skin more easily, and in young animals they pene- 

 trate more easily into the orifices of the hair follicles. Certain 

 skin diseases (eczema, sarcoptic scab) as well as distemper also 

 increase the susceptibility to a certain degree. In contrast to 

 the frequency of the eruption, the artificial transmission of the 

 disease to healthy animals has succeeded only rarely, and at 

 most a transitory skin affection occurred after rubbing in pus 

 containing the mites (Haubner, Cornevin) ; only Guinard suc- 

 ceeded in producing the disease in its typical form in a young 

 dog. It is not a rare occurrence that some dogs of the same 

 breed and kept under like conditions are not infected 1)}^ their 

 companions. For the infection to occur, certain predisposing 

 circumstances not yet known are evidently of influence. 

 (Prietscli observed contagion of a billy goat and a deer from a 

 dog.) 



Pathogenesis. The hair follicle mites penetrate through the 

 orifice of the hair follicle, and subsequently also into the regional 

 sebaceous glands ; they increase there so that their number in a 

 hair follicle or sebaceous gland may amount to from 30 to 60 

 (Friedberger) and even 100 to 200 (Gruby). They occur mostly 

 in all parts of the hair follicle and sebaceous gland and lie almost 



