24 THE DATA OF BIOLOGY. 



duced to less coherent forms of asraregation ; there is reason 

 to think that this same inertia facilitates changes of arrange- 

 ment among their constituent atoms; since, in proportion as 

 an incident force impresses but little motion on a mass, it is 

 the better able to impress motion on the parts of the mass in 

 relation to each other. And it is further probable that the 

 extreme contrasts in molecular mobilities among the compo- 

 nents of these highly complex atoms, aid in producing modi- 

 liability of arrangement among them. 



Lastly, the great difference in diffusibility between colloids 

 and crystalloids, makes possible in the tissues of organisms, 

 a specially rapid re-distribution of matter and motion ; both 

 because colloids, being easily permeable by crystalloids, can 

 be chemically acted on throughout their whole mass, in- 

 stead of only on their surfaces ; and because the products of 

 decomposition, being also crystalloids, can escape as fast as 

 they are produced, leaving room for further like transforma- 

 tions. So that while the composite atoms of which organic 

 tissues are built up, possess that low molecular mobility fit- 

 ting them for plastic purposes, it results from the extreme 

 molecular mobihties of their ultimate constituents, that the 

 waste products of vital activity escape as fast as they are 

 formed. 



To all which add, that the state of warmth, or increased 

 molecular vibration, in which all the higher organisms are 

 kept, increases these various facilities for re-distribution : not 

 only as aiding chemical changes, but as accelerating the dif- 

 fusion of crystalloid substances. 



