358 BOVINE PATHOLOGY. 



the surface, forming crusts, whicli are liable to be succeeded 

 by ulceration. The hair falls off, or a few hairs persist and 

 project from the crusts. In chronic cases there is but little 

 irritation, but the skin is thickened, devoid of sensibility, 

 dry, harsh, and corrugated. " Thus, it will be observed, 

 no special symptoms indicate mange j it passes through 

 several stages — papular, vesicular, &c. Diagnosis must de- 

 pend, in the first place, upon detection of the parasites; also, 

 secondly, upon accurate tracing to an origin by contagion. 

 The latter must be, for we cannot allow that animals so 

 high in the scale as Acari can appear spontaneously. The 

 spontaneous origination of the disorder was once uni- 

 versally allowed, but this depended upon confusion of 

 mange with some of the simple non-parasitic diseases 

 already described, or hon-recognitiori of the presence of 

 parasites. This disease, in regularity of eruption, phases, 

 persistency, and contagiousness, resembles some of the 

 eruptive disorders of the system. Analogy leads us to 

 anticipate that the latter will, with improved means of in- 

 vestigation, be traced to parasitic forms of some kind or 

 other. This lesson learned from mange is a remarkable one. 

 When the disease is unchecked it exhibits urgency pro- 

 portioned to the seasons or the surrounding temperature. 

 Thus, it seems to be dormant in the winter, but in warm 

 weather and places is almost intolerable. The disease is 

 not truly transmissible to the attendants and to animals 

 of other species, for the parasites cause inconvenience for 

 a time but do not propagate in their new abode. The 

 Acari can be detected on the hairs and surface of the 

 epidermis, and can be seen with the naked eye as minute 

 white points moving about somewhat rapidly when the 

 patient stands in the full glare of the sun. Gerlach, who 

 is one of the leading authorities on this subject, suggests 

 for detection of Dermatodectes the removal of some of the 

 scales from the surface and placing them on the human 

 arm, with the under part uppermost, for an hour or more. 

 The Acari pass to the arm and there cause eruption, and 

 when the vesicles form they may be punctured with a needle 

 and the parasite obtained. Subsequently the arm should 



