286 POISONING BY MERCURIAL VAPOURS 



results. To this acidulated solution hydrogen sulphide, 

 cautiously added, throws down a white precipitate (HgCl 2 -f 

 2HgS), which, on further addition of the precipitant, becomes 

 brown and then black (HgS), and is insoluble in dilute acids 

 and ammonium sulphide. Caustic potash yields a yellow 

 precipitate of oxide (HgO), insoluble in excess. Potassium 

 iodide gives a precipitate yellow at first, but rapidly becom- 

 ing red (HgI 2 ), soluble in excess of the potassium salt. 



ACTIONS AND USES. Mercury, mercurous salts, and 

 mercuric salts differ in their local effects, largely depending 

 on their solubility. Metallic mercury has no topical irritant 

 action, but is slowly absorbed, and produces its general 

 effects if finely divided, as in the case of mercurial ointment, 

 or in the state of vapour. The chief mercurous salts are 

 insoluble in water, and are but slowly dissolved by the 

 tissues. Hence they have a very slight topical action, and 

 are only slowly absorbed. But the more soluble mercuric 

 salts readily unite with albumin, the albuminate is dissolved 

 by excess of proteid, and so these salts are corrosive, act as 

 irritant poisons, and are quickly absorbed. When ab- 

 sorbed, all mercurials produce, however, the distinctive 

 actions of the drug, and if continued, the condition of 

 mercurialism. Calomel, grey powder, and blue pill, are 

 prescribed to develop mild mercurialism, to lessen putre- 

 faction in the intestine, and to act as purges. They are 

 cathartics, increasing both secretion and peristalsis by the 

 irritation they set up, and especially when conjoined with 

 a small amount of any cathartic. They are also diuretic. 

 Corrosive sublimate, the biniodide, and the double cyanide 

 of mercury and zinc are effectual germicides. Ointments of 

 mercury and of mercuric iodide are applied as antiparasitics, 

 absorbents, and counter-irritants. Mercurials are excreted 

 chiefly by the kidneys and intestine, but also in the saliva, 

 bile, and sweat. They pass into the milk of nursing females ; 

 and Gasparin has seen lambs die from mercurialism when the 

 ewes had been freely dressed with ointment. Elimination 

 begins tolerably rapidly, but is slow and irregular, and is 

 often not completed for months after administration has 

 ceased. 



Mercury, so long as it remains uncombined, like other 



