104 THE THEORY OF IONS 



loids are also ionisable and have a similar mode of 

 action. Many of the non-ionisable therapeutic 

 agents, as narcotics, sedatives and bactericides, have, 

 through their ester-like structure, an intimate rela- 

 tion with the lipoids of the cells and become ionised 

 by combining with them. In this way an anion is 

 liberated by which the pharmacological effect is 

 produced. Just as the non-ionised compound finds 

 its selective point in the lipoids, so the ionised ones 

 find their point of attack in the proteins, " and a 

 difference in the distribution or a replacement of 

 the normal ions of the cell would be connected with 

 changes in the state of the colloids and consequently 

 of their functions."* 



The influence of ions upon physiological functions 

 such as growth, irritability and life itself, is of im- 

 portance not only to the biologist but to the patho- 

 logist, especially in connexion with the subject of 

 disinfection. The experiments of Loeb have been 

 already referred to ; it was he who first observed 

 that certain ions were toxic and others antitoxic to 

 living tissues. The fertilised eggs of Fundulus 

 magellus develop equally well in distilled water or 

 in sea-water. If however the eggs were put into 

 a solution of NaCl of the same strength as sea-water 

 they all died in a few hours. But if a small amount 

 of calcium chloride, a constant constituent of sea- 

 water, be added, the development proceeds and 

 normal embryos are produced. The sodium is toxic 

 and the calcium ion antitoxic. This is an instance 



* Pauli's " Physical Chemistry in the Service of Medicine," 

 p. 86. 



