GENERAL ACTION OF IRON AND ITS SALTS 185 



Internal. — Alimentary Canal, — Iron is a food rather than 

 a medicine. It exists as a natural constituent of vegetable 

 foods and of the body, and is found particularly in the 

 haemoglobin of the blood — to the extent of about half an 

 ounce in that of the horse. There is a sufficient quantity in 

 the food to support healthy animals. If iron is given to a 

 normal animal, it has little effect unless continued for a long 

 time in considerable quantity, when it may produce indiges- 

 tion and constipation. 



The iron salts and iron itself have practically the same 

 physiological action, but some preparations are more 

 irritating and astringent in the digestive tract than others. 

 Ferric chloride and ferrous sulphate are particularly consti- 

 pating; while reduced iron, the oxide, carbonate, and salts 

 of the vegetable acids, are slightly so. Iron may blacken 

 the tongue from formation of the sulphide. In the stomach 

 all forms of iron are converted into ferric, and, to a slight 

 extent, ferrous chloride, by the gastric juice. Strongly acid 

 salts are decomposed and the combined acid in the salt is 

 set free, owing to the formation of the chloride. This acid 

 may prove irritating to the mucous membrane of the 

 stomach. Acid salts, as the sulphate, are, therefore, more 

 suitable for the horse than for the dog, as the latter is more 

 susceptible to the irritating action. Ferric salts being 

 astringent, so all the iron salts possess some astringency 

 when they are converted into ferric chloride in the stomach. 

 But those preparations most astringent outside of the body, 

 are also most astringent in the digestive canal, from the 

 fact that as only part of the dose is normally changed into 

 the chloride in the stomach, the balance of the dose (if 

 already astringent), increases the astringency of the chloride 

 formed in the stomach. 



The iron salts, on entering the bowels, come into con- 

 tact with an alkaline medium. None of the iron is absorbed, 

 but escapes in the faeces (as the sulphide), coloring the dis- 

 charges black. If none of the iron given as medicine is 

 absorbed, how is the body benefited thereby? Bunge's 



