350 PHYSIOLOGICAL DEVELOPMENT. 



going the isomeric change, predominate, but have scattered 

 through them the other molecules out of which they may be 

 formed, either by composition, or modification. That is to 

 say, a wave of molecular disturbance diffused from a centre, 

 and travelling furthest along a line where lie most molecules 

 that can be isomerically transformed with facilit}^ will be 

 likely at the same time to further differentiate this line, and 

 make it more characterized than before by the eas}^ -trans- 

 formability of its molecules. One additional step, 



and the interpretation is reached. Analogy shows it to be 

 not improbable that these organic colloids, isomerically trans- 

 formed by slight molecular impact or increase of molecular 

 motion, will some of them resume their previous molecular 

 structures after the disturbance has passed. We know that 

 what are stable molecular arrangements under one degree of 

 molecular agitation, are not stable under another degree; and 

 there is evidence that re-arrangements of an inconspicuous 

 kind are occasionally brought about by very slight changes 

 of molecular agitation. Water supplies a case. Prof. 

 Graham infers that water undergoes a molecular re-arrange- 

 ment at about 32'* — that ice has a colloid form as well as a 

 crystalloid form, dependent on temperature. Send through 

 it an extra wave of the molecular agitation we call heat, and 

 its molecules aggregate in one way. Let the wave die away, 

 and its molecules resume their previous mode of aggregation. 

 And obviously such transformations may be repeated back- 

 wards and forwards within narrow limits of temperature. 

 Now among the extremely unstable organic colloids, such a 

 phenomenon is far more likely to happen. Suppose, then, that 

 the nerve-colloid is one of which the molecules are changed in 

 form by a passing wave of extra agitation, but resume their 

 previous form when the wave has passed : the previous form 

 being the most stable under the conditions which then recur. 

 What follows ? It follows that these molecules will be ready 

 again to undergo isomeric transformation when there igain 

 occurs the stimulus ; will, as before, propagate the transform a- 



