352 MANUAL OF EQUINE MEDICINE. 



at regular intervals. The symptoms presented were to be 

 attributed to this practice, as the horse always enjoyed 

 perfect health previously, and made much improvement 

 when the groom left. 



Diagnosis. — The history of the case will aid us in forming 

 a diagnosis in some instances. 



The thread-like character of the pulse, and the purging 

 with extreme tenesmus in severe cases, will assist us in 

 diagnosing acute arsenic poisoning from enteritis. 



Detection of Poison. — In the solid state arsenious acid 

 may be detected by the following tests : 



(1.) When heated on platinum foil arsenious acid pro- 

 duces a white vapour, and is entirely volatilized. 



(2.) If some of the powder be heated in a small test-tube 

 it will be sublimed, and small octahedral crystals, visible to 

 the naked eye or by a lens, settle on the sides of the tube. 



(3.) If arsenious acid be mixed with freshly burnt 

 powdered charcoal, and heated in a small test-tube, a ring 

 of shining metallic arsenic of a grey colour will be found on 

 the cool portion of the tube, and an odour of garlic is per- 

 ceptible. 



If this deposit be heated it will become oxidized, and 

 octahedral crystals of arsenious acid formed. 



Further, the arsenious acid may be dissolved in distilled 

 water and the liquid tests applied to the solution. 



In solution arsenious acid may be detected by several 

 tests. The solution of it in water is colourless, almost taste- 

 less, and has a very slightly acid reaction. If a few drops 

 be evaporated on a glass slide and examined by the micro- 

 scope, numerous minute, and mostly imperfect, octahedral 

 crystals of an amorphous deposit will be seen, presenting 

 triangular surfaces by reflected light. 



(1.) The ammonio-nitrate of silver (prepared by adding 

 a few drops of liquor ammonise to a solution of nitrate of 



