Ill] OF RATE OF ACTION 81 



The difference between the two classes of phenomena is akin to 

 the difference between the forces which determine the form of a 

 raindrop and those which, by the flowing of the waters and the 

 sculpturing of the solid earth, have brought about the configuration 

 of a river or a hill ; molecular forces are paramount in the one, and 

 wolar forces are dominant in the other. 



At the same time, it is true that all changes of form, inasmuch 

 as they necessarily involve changes of actual and relative magnitude, 

 may in a sense be looked upon as phenomena of growth ; and it is 

 also true, since the movement of matter must always involve an 

 element of time*, that in all cases the rate of growth is a phenomenon 

 to be considered. Even though the molecular forces which play 

 their part in modifying the form of an organism exert an action 

 which is, theoretically, all but instantaneous, that action is apt to 

 be dragged out to an appreciable interval of time by reason of 

 viscosity or some other form of resistance in the material. From 

 the physical or physiological point of view the rate of action may be 

 well worth studying even in such cases as these; for example, a 

 study of the rate of cell-division in a segmenting egg may teach us 

 something about the w^ork done, and the various energies concerned. 

 But in such cases the action is, as a rule, so homogeneous, and the 

 form finally attained is so definite and so little dependent on the 

 time taken to effect it, that the specific rate of change, or rate of 

 growth, does not enter into the morphological problem. 



We are deahng with Form in a very concrete way. To Aristotle 

 it was a metaphysical concept; to us it is a quasi-mechanical effect 

 on Matter of the operation of chemico-physical forces f. To 



* Cf. Aristotle, Phys. VI, 5, 235a, 11, eirel yap awaaa Kiurjffis ev XP^'^V* kt\.; he had 

 already told us that natural science deals with magnitude, with motion and with 

 time: ^<ttiu ij irepl (pvaeus eiriar-qtnj irepl fxiyedos Kai klvt^ctlv koL xP^^^^- Hence 

 omnis velocitas tempore durat became a scholastic aphorism. Bacon emphasised, in 

 like manner, the fact that "all motion or natural action is performed in time: 

 some more quickly, some more slowly, but all in periods determined and fixed in 

 the nature of things. Even those actions which seem to be performed suddenly, 

 and (as we say) in the twinkling of an eye, are found to admit of degree in 

 respect of duration" {Nov. Organon, xlvi). That infinitely small motions take 

 place in infinitely small intervals of time is the concept which lies at the root of the 

 calculus. But there is another side to the story. 



t Cf. N. K. KoltzotF, Physikalisch-chemische Grundlage der Morphologie, 

 Biol. Centralbl. 1928, pp. 345-369. 



