III. IONS IN BIOLOGY 



THERE is abundance of evidence that electrical 

 changes are an important item in biological pro- 

 cesses, that chemical substances are built up as 

 well as broken down in living tissues, that living 

 substances are organised and disorganised. How 

 far the theory of ions may account for the changes 

 that take place in living tissues and to what extent 

 ionisation is responsible for them is at present 

 unknown. But that ionisation takes place in living 

 structures and the presence of ions therein influences 

 biological processes is evident. On purely theoreti- 

 cal grounds Nageli* considered that the essential 

 substance of protoplasm, that is the living substance, 

 must consist in its ultimate structure of ultra- 

 microscopical solid particles or systems of such 

 particles surrounded by material of a fluid con- 

 sistence. He supposed that such particles, acting 

 like substances known as ferments or enzymes, 

 produced chemical changes in the materials with 

 which they are brought in contact, without being 

 themselves materially changed. McKendrickf of 

 Glasgow said in a lecture : " When cells were exam- 

 ined by the highest microscopical powers they did 

 not seem to have advanced far towards an explana- 



* Quain's "Anatomy," vol. i., part ii., "Histology." 

 t Brit. Med. Jour., 1901, ii., 817. 

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