22 THE DATA OF BIOLOGY. 



matters, are probably materials for decomposition ; and some, 

 as carbonic acid, water, urea, kreatine, and kreatinine, are 

 products of decomposition. Into the mass of mingled colloids, 

 mostly insoluble and where soluble of very low molecular 

 mobility or diffusive power, we have constantly passing, crys- 

 talloids of high molecular mobility or diffusive power, that 

 are capable of decomposing these complex colloids ; and from 

 these complex colloids, so decomposed, there result other 

 crystalloids (the two chief ones extremely simple and mobile, 

 and the rest comparatively so) which diffuse away as rapidly 

 as they are formed. 



And now we may clearly see the necessity for that pecu- 

 liar composition which we find in organic matter. On the 

 one hand, were it not for the extreme molecular mobihty 

 possessed by three of its chief elements out of the four ; and 

 were it not for the consequently high molecular mobility of 

 their simpler compounds ; there could not be this quick escape 

 of the waste products of organic action ; and there could not 

 be that continuously active change of matter which vitality 

 implies. On the other hand, were it not for the union of 

 these extremely mobile elements into immensely complex 

 compounds, having relatively vast atoms that are made com- 

 paratively immobile by their inertia, there could not result 

 that mechanical fixity which prevents the components of liv- 

 ing tissue from diffusing away along with the effete matters 

 produced by the decomposition of tissue. 



§ 9. Thus in the substances of which organisms are com- 

 posed, the conditions necessary to that re-distribution of 

 Matter and Motion which constitutes Evolution, are fulfilled 

 in a far higher degree than at first appears. 



The mutual aflinities of the chief organic elements are 

 not active within the limits of those temperatures at which 

 organic actions take place ; and one of these elements is 

 especially characterized by its chemical indifference. The 

 compounds formed by these elements in ascending grades of 



