12 VETERINARY TOXICOLOGY 



that the ions do not possess the ordinary properties of their 

 components. It is only when the ions are discharged, as in 

 electrolysis, or in the course of a chemical reaction, that the 

 ordinary properties of the element or group are displayed. 

 To suppose, for instance, that the existence of the sulphate 

 ion SO4" in a solution of magnesium sulphate in the least 

 degree confers the properties of ordinary sulphuric acid on 

 the solution may prove most misleading. 



The existence of SO4 ions in a solution, together with 

 metal ions, such as those of magnesium, zinc, and sodium, 

 means that we have to do with a salt solution. In ordinary 

 sulphuric acid solution we have whole molecules of 

 H28O4 and ions of SO4 and hydrogen, all in proportions 

 determined by the concentration. Similarly with other 

 acids, such as nitric and hydrochloric, in solutions of which 

 we have ions of hydrogen, and of NO3 and chlorine, respec- 

 tively. The existence of hydrogen ions in a solution means 

 the possession of acid properties. Alkalis, such as caustic 

 potash, KOH, ionise into K ion and OH ion, and similarly 

 with other alkalis, and the existence of alkalinity in a solu- 

 tion is a fact parallel with the existence of OH or hydroxyl 

 ions in it. 



The simple physical laws of osmosis, in accordance with 

 which a dissolved crystalloid tends to permeate the mem- 

 brane, passing from the more to the less concentrated 

 solution, adequately accounts for the absorption of dissolved 

 alkaloids and organic poisons, which do not exercise local 

 chemical reactions. If on the one side we have a solution 

 of strychnine, and on the other a liquid free of that 

 substance, the alkaloid will traverse the membrane. If the 

 solution into which it passes is not removed, equilibrium 

 will be established when the solutions on both sides are of 

 the same strength, but if, as in the digestive system, this 

 solution is continually removed, the osmosis will go on to 

 completion. 



The intestinal epithelium is semi-permeable to some 

 salts, and, for example, will not allow of the passage of the 

 magnesium ion. This metal is, therefore, not absorbed from 



