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domain of this branch of physics. The minute structure of many of the workings of the molecules of the body are directly concerned with this subject.
As early as the year 1866, Dr George Wilson, then professor of Technology in Edinburgh University, pointed out[1] the remarkable physical properties of the elements composing organized bodies, and especially mentioned phosphorus, nitrogen and iron, and their compounds, as instances of the 'mobility' and adaptation of these elements to the varied wants of the body.
Thus, phosphorus, in virtue of its changeableness, "may occur in the brain in the vitreous form, changing as quickly as the intellect or imagination demands, and literally flaming that thoughts may breathe or words may burn; or it may be present in the bones in the amorphous form, content, like an impassive caryatid, to sustain upon its unwearied shoulders the mere dead weight of stones of flesh." It is thus also "that the mobility of nitrogen makes it pre-eminently the modifier of the living organism; like a half-reclaimed gipsy from the wilds, it is ever seeking to be free again, and not content with its own freedom is ever tempting others not of gipsy blood to escape from thraldom.
Mr Herbert Spencer[2] also has recently extended these remarks to the chief organic compounds of the body, showing that both binary and ternary compounds are isomeric and polymeric to a high degree, and exhibit a low stability, readily decomposing when subjected to either physical or chemical influences. But it is to Dr Graham that we owe the chief advance in our knowledge of the subject. He had long ago noticed the remarkable variations in the mobility of different gases — and now he has put forth his remarkable generalizations respecting the 'crystalloid' and 'colloid' constitution of bodies. I have elsewhere[3],
