INTRODUCTION 7 



The gaseous state represents the most easily absorbable of 

 all forms, when the gas enters the lungs. The very rapid 

 action of gases, such as hydrocyanic acid, carbon mon- 

 oxide, sulphuretted hydrogen, and volatile ansesthetics— e.pf., 

 chloroform ether and nitrous oxide — illustrates this point. 



Solids insoluble in water, in dilute acids, or in dilute 

 alkalis, in general are not poisonous by the alinientary 

 tract. Thus, the soluble salts of barium are very poison- 

 ous, but barium sulphate is insoluble and non -toxic. 

 With lead sulphate the insolubility is not so pronounced, 

 and therefore it has a definite though slow toxic action. 

 Perhaps the best instance is that of arsenious oxide. 

 When the coarsely powdered vitreous substance is freed 

 from impalpable particles, large quantities may be given to 

 dogs without bad effect. 



Solutions or solids soluble in the body fluids are easily 

 absorbed from the alimentary tract, provided that they are 

 not precipitated — e.g., by acid, or alkali, or albumin — and 

 that they are diffusible by osmbsis — i.e., can permeate 

 animal membranes. Thus, a solution of arsenious oxide, 

 or of an alkaloid, is a readily absorbable and diffusible 

 substance, but a dilute solution of silver nitrate is mainly 

 precipitated as the insoluble silver chloride by the hydro- 

 chloric acid of gastric juice. The absorption of an 

 alkaloid is retarded by the formation of the insoluble 

 tannate when tannin is employed as a remedial agent, 

 and most of the heavy metal salts give precipitates of 

 insoluble albuminates whereby absorption is retarded. 

 Toxines (except ricine and crotine) are not, or only very 

 slowly, diffusible, and therefore not absorbed by the intact 

 membranes. They are thus not toxic by the alimentary 

 tract, or, like ricine, act far less intensely in this way. 

 Another example of a soluble poison which is not easily 

 absorbed is afforded by the alkaloid curarine. Moreover, 

 the living cell wall is impermeable to certain dissolved 

 substances — thus to the magnesium radicle, or ion, in 

 solution — so that that metal is not absorbed from the 

 stomach or intestines. 



