64 VETEEINARY TOXICOLOGY 



zinc ferrocyanide by means of potassium ferrocyanide from 

 neutral solutions, or in the presence of acetic acid. 



As a point of medico-legal value, it may be observed that 

 traces of zinc are very often found in alimentary contents, 

 but must not be taken as indicative of poisoning in the 

 absence of concordant symptoms and lesions. When, how- 

 ever, the metal is found in the liver, there are stronger, 

 though not absolutely conclusive grounds for suspicion. 



SILVER. 



Forms and OccuFPence. — Metallic silver is not important 

 from the standpoint of pharmacy and toxicology. The 

 commonest soluble compound is the nitrate, very easily 

 soluble in water, and stable on heating, being fused and cast 

 into sticks for use as lunar caustic. The halogen salts (the 

 chloride and bromide) are very extensively used in photog- 

 raphy, but are not dangerous. The very dangerous 

 cyanide is also used in photography and largely in silver 

 plating. Colloidal silver is the metal reduced in the presence 

 of solutions of colloids, and is soluble. It is used in 

 medicine, and, like the organic salts the lactate or actol, and 

 citrate or itrol, does not act as an irritant. An efficacious 

 non-irritant silver preparation is jyrotargol, a compound of 

 silver with albumose. 



Poisoning by silver is rare, and the acute form follows the 

 administration of large doses of soluble salts. Accidents in 

 the case of the dog may result from the swallowing of a 

 stick of lunar caustic. Smaller and repeated doses give 

 rise to the condition known as argyria. 



Absopption. — Soluble salts of silver form albuminates 

 like those of the heavy metals, and these are but slowly 

 absorbed. The astringent and caustic actions of the nitrate 

 are thus confined to the parts in contact. In the stomach 

 the salts are decomposed by the hydrochloric acid giving 

 silver chloride, which is very sparingly soluble in acids and 

 water, but slightly dissolved by sodium chloride solution. 



