24 THE THEORY OF IONS 



found that the anion OH is rather more toxic to 

 moulds than the cation H ; and the toxicity of the 

 anions Cl, Br and I, increases slightly with their 

 atomic weight. The ion of cyanogen radical is 

 powerfully poisonous to fungi, and potassium 

 cyanide has nine times more toxicity than that of 

 HC1. Mercuric chloride and silver nitrate are about 

 equally toxic to moulds, and are followed closely 

 by potassium dichromate, potassium chromate, and 

 formaldehyde. In many cases the dissociation 

 lessens the toxic effects. Out of eight acids, six 

 were more toxic in the molecular than in the ionised 

 form. The anions of mineral acids have a low toxic 

 value for fungi : those of HC1, HN0 3 , and H 2 S0 4 

 have a toxicity of less than -^ that of H ions. The 

 undissociated HCN molecule has a toxicity 76-6 

 times that of H ions ; that of acetic acid 2-8 times 

 that of H ions ; but when the hydrogen in acetic 

 acid is replaced by chlorine the toxicity increases, 

 but the dissociation increases also and the two 

 effects partially balance one another.* 



Chloride of sodium is toxic to many low-formed 

 organisms, and to contractile tissues generally. 

 Thus, fundulus ova will develop in distilled water, 

 but not in water which only contains sodium 

 chloride ; if, however, some calcium chloride also 

 be added to the water the development proceeds 

 normally ; from which it is inferred that sodium ions 

 are toxic, but calcium ions anti toxic, f Strontium 

 ions have the same antitoxic effect as calcium ions. 



What influence has ionisation upon muscular 



* Clarke : loc. cit. 



t Osborne : Proc. Physiol. Soc., 1905, x.-xii. 



