630 THE MECHANISM OF ABSORPTION 



whole group of drugs which act somewhat like barium chloride, 

 e.g. digitalis suprarenal, &c., can be antagonised largely by Ca salts. 

 The same is true of the purgative cascara and of some bacterial 

 haemolysins. Such observations suggest the possibility that the 

 antagonistic action of ions might be of a chemical nature. And 

 this was supposed to be the case until Loeb made the important 

 suggestion that it was the valency of the cation which determined 

 antitoxic action. Loeb started at least two views to account for 

 his own observations on antitoxic action, and left the subject in a 

 condition of great uncertainty, which still exists more or less in 

 spite of the recent work of Mathews and Lillie. It is possible to 

 give here only the general conclusions at which Mathews has 

 arrived. According to his view the physiological action or toxicity 

 of a salt is due to the sum of the solution tension and not to the 

 valency of its ions, that is to say, toxicity is a property of both 

 ions. Similarly, he believes that the antitoxic power of a salt is a 

 property of both its ions, and is not confined to an antagonism 

 between cations of different valency, as Loeb thought. It is as 

 yet uncertain what determines the antitoxic power of a salt ; for 

 it is not in all cases known to be related to the sum of the 

 solution tensions of the ions. 



When we try and get an insight into the way in which salts 

 exert their toxic and antitoxic powers on bioplasm, we find that 

 our knowledge is extremely meagre. The experimental evidence 

 is confined largely to observations on the ova and ciliated larvae 

 of marine animals. The observations show that the toxic action 

 of a salt may be associated with the following gross changes in 

 bioplasm, (a) Plasmolysis. Many salts, such as NaCl, KC1 and 

 Lid, are toxic to ova when the osmotic pressure of their solutions 

 is greater than that of sea- water. The egg membrane is relatively 

 impermeable to those salts, and if the osmotic pressure outside is 

 sufficiently great, the cell undergoes plasmolysis. A calcium salt 

 is able to neutralise this action completely by altering apparently 

 the permeability of the membrane to the toxic salt ; in this way 

 the effective osmotic pressure of the toxic solution is reduced and 

 plasmolysis prevented. (&) Coagulation. Other salts, such as 

 those of Mn, Co, Ni, are toxic in concentrations far lower than 

 would be necessary to produce plasmolysis of the cell. The salts 

 produce a slow coagulation of the cell contents owing to the 

 gradual passage of the salt through the egg membrane. The 



