THE MITES 107 



gether with a few flakes from the deeper portion of the crust, may then 

 be placed upon a glass and teased in glycerin. After having been 

 sufficiently divided and spread by the needles, it is ready for examination 

 imder the low power of the microscope, or by a strong hand lens. It is 

 often necessary to thoroughly search several preparations before finding 

 the acarus. The material can be more easily teased and cleaned up if 

 submitted for an hour or two to the action of a five to ten per cent, 

 solution of caustic soda. 



A method commonly used in the Laboratory of the Pennsylvania 

 State Bureau of Animal Industry for the detection of scab acari is as 

 follows: Cover the material with a ten per cent, solution of sodium 

 hydrate and set aside for one or two hours. Heat to boiling and cen- 

 trifuge for twenty minutes. The liquid is then carefully drawn off, 

 water added, and the sediment shaken up. This is again centrifuged, 

 water drawn off, and fresh water added in which the sediment is again 

 washed and centrifuged. The sediment is then thinly spread upon 

 slides and examined under low power. By this treatment the scabs and 

 crusts are thoroughly disintegrated. Some of the mites may also be 

 fragmental, but not to such an extent as to prevent recognition of the 

 species. 



Prognosis. — Owing to its great contagiousness and the difficulty in 

 reaching the parasites, sarcoptic acariasis is the most serious of the 

 three forms which may affect the horse. Early in its course the con- 

 stantly tortured and unpresentable animal becomes unfit for work, and, 

 when the disease is advanced, the skin lesions are accompanied by 

 anaemia, emaciation, and a general debility that may terminate in death. 

 As in other parasitic skin diseases, vigorous animals in good condition 

 are more resistant and are more easily cured than those unthrifty or old 

 and emaciated. 



Transmission. — The transmission of mange from horse to horse or 

 to asses and mules takes place by contact of individuals and by numerous 

 ways in which the parasite can be transported, as by litter, grooming 

 utensils, harness, clothing, or any object upon which the affected animal 

 has rubbed. Its contagion is modified considerably in relation to the 

 stage of the disease. Early in its course the acari have little tendency 

 to leave their host, but after one or two generations, with the formation 

 of the typical skin lesions, they emigrate readily, either directly or in- 

 directly, from one animal to another. 



Mange of the horse can be transmitted to man and, reciprocally, 

 that of man to the horse, though such cases are rare. In either event the 

 parasite does not find a favorable soil for its multiplication, and the 

 invasion is but transient, such affection as it produces usually yielding 

 promptly to treatment or spontaneously disappearing in a few weeks. 

 It is doubtful whether this mange can be communicated to other animals; 



