GEKLACH ON THE ITCH AND MANGE. 161 



and unproductive seasons, and the severity of mange in cer- 

 tain years can be attributed as little to changes in the 

 weather, vegetation, &c., as the spread of plagues or epizo- 

 otics can be imputed to diet, pasturage, &c." 



A question of immediate practical importance is the find- 

 ing of acari on animals, and we therefore transcribe Gerlach's 

 interesting remarks on the subject. Gerlach says: "The 

 finding these insects has, as yet, been attended with great 

 difficulty; in man, however, it is easily done by following 

 the little grooves upon fresh papulae, and especially in the 

 larger tracts, at the blind end of which there may or may 

 not be nodules or vesicles. It has not been possible hereto- 

 fore for veterinary surgeons to discover these parasites with 

 certainty, because the various insects and their chief charac- 

 ters have not been known, and they have not been regarded 

 as the ontological cause of scabies." The various procedures 

 to find the acari are as follows : 



1. Animals are placed in the sun and carefully examined ; 

 the acari do not get on the surface of the epidermic scales and 

 on the hairs as dermatodectes do, and these can be seen with 

 the naked eyes. 



2. The sarcoptes are found below the scales or scabs, 

 which may be so adherent to the skin, that, on being re- 

 moved, the latter may bleed. The dermatodectes are 

 observed after the animals have been exposed to the sun, on 

 the outer part of these scales, but the sarcoptes are only 

 seen on the inner. The scales examined should always be 

 fresh, and they may be laid on black paper in a warm place 

 in the sun, and then examined by a weak lens embracing a 

 wide field of view. The small sarcoptes are only discovered 

 when the cuticle has been removed with the scab. 



3. The sarcoptes are most certainly and easily found when 

 VOL. n. 3 E 



