MINEEAL OE INOEGANIC POISONS 43 



must be verified by heating the coated copper in a dry 

 tube, when the cooler parts of the tube become coated 

 with a glistening white crust, which shows the octahedral 

 crystalline form under a low power, and by solution from 

 the copper by means of pure sodium hydrate and hydrogen 

 peroxide, or by pure sodium peroxide, and submitting the 

 solution to the well-known Marsh test. The quantitative 

 estimation of arsenic is usually performed by comparing 

 the size of the mirror got in Marsh's test with sealed 

 standard mirrors prepared from known quantities of arsenic. 

 In this way absolutely indisputable evidence of the presence 

 of arsenic may be obtained, and chemical diagnosis is a 

 matter of certainty, with the single exception of the rare, 

 though theoretically possible, case where death is just 

 produced by a dose of such magnitude that the elimination 

 of the last trace of the poison coincides with the time of 

 death. 



Medico-Legal, — It has been held that arsenic remains 

 longest in the bones, and that it may be found in the hair. 

 It may be recognised a very long time after death, but in 

 cases of analysis of exhumed parts care is needed to exclude 

 the possibility of arsenic having entered in traces from the 

 soil. 



In all analysis it is necessary to prove by blank experi- 

 ment that the apparatus and chemicals used are free of 

 arsenic. 



The actual proportions found in practice vary very widely ,- 

 as may be expected. The greatest proportion is often that 

 noted in the crop contents of fowls. In cattle arsenic has 

 been observed in the varying proportions of 4 grains to 

 xlg- grain per ounce of ingesta, and it will be clear that 

 these figures refer to the excess of poison, and bear no 

 definite relation either to the original dose or to that 

 absorbed part by which poisoning was caused. In those 

 cases where the greater part of the dose is rejected by 

 vomiting, recovery may occur ; but, if death ensues, arsenic 

 is generally to be found in the stomach walls and liver. 



Unless the quantity of arsenic actually separable from 



