MYSTERIES OF LIFE AND MIND 



role. But such views opened the way to simple 

 mechanical conceptions of the processes of sen- 

 sation. 



When Dr. Loeb had shown that frog's muscles 

 might be made to beat or stop under the influence 

 of certain ions, it was but a step to suppose that 

 these same ions might have an equal effect on the 

 tissue of the nerves. That step was taken by 

 Dr. Albert P. Mathews, a colleague with Professor 

 Loeb, who had come back to his native city of 

 Chicago after a varied wander jahr, to take the post 

 of physiological chemistry in its university. 



A mass of observation and experimental material 

 was already at hand. Half a century ago Thomas 

 Graham, a highly original English chemist, struck 

 out a broad line of distinction between those sub- 

 stances which crystallize when they solidify and 

 those which do not. The latter he called the col- 

 loids, the gluelike substances. An ordinary hen's 

 e gg r gelatine, are good examples. When the 

 cook stirs up fat or jelly in hot water she makes 

 a colloid solution. Speaking broadly, the human 

 body is such an affair. That is, it is about seventy- 

 five per cent, water, the rest jelly and bones. The 

 nerves and the brain cells are eighty or eighty-five 

 per cent, water. 



The action of the colloids in water was long a 

 bothersome puzzle. Much light came when Hardy, 



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