14 THE DATA OF BIOLOGY. 



compounds^ that take the leading part in organic actions. 

 According to Mulder, the formula of albumen is 10 (C^ H^^ 

 W O^^) + S^ P. That is to say, with the sulphur and phos- 

 phorus there are united ten equivalents of a compound atom 

 containing forty atoms of carbon, thirty-one of hydrogen, 

 five of nitrogen, and twelve of oxygen : the atom being thus 

 made up of nearly nine hundred ultimate atoms. 



§ 5. Did space permit, it would be useful here to consider 

 in detail, the interpretations that may be given of the pecu- 

 liarities we have been tracing : bringing to their solution, 

 those general mechanical principles which are now found to 

 hold true of molecules as of masses. But it must suffice 

 briefly to indicate the conclusions that such an inquiry pro- 

 mises to bring out. 



Proceeding on mechanical principles, it may be argued that 

 the molecular mobility of a substance must depend partly on 

 the inertia of its molecules ; partly on the intensity of their 

 mutual polarities ; partly on their mutual pressure, as deter- 

 mined by the density of their aggregation, and (where the 

 molecules are compound) partly on the molecular mobilities 

 of their component molecules. Whence it is to be inferred 

 that any three of these remaining constant, the molecular 

 mobility will vary as the fourth. Other things equal, there- 

 fore, the molecular mobility of atoms must decrease as their 

 masses increase ; and so there must result that general pro- 

 gression we have traced, from the high molecular mobility 

 of the uncombined organic elements, to the low molecular 

 mobility of those large-atomed substances into which they are 

 ultimately compounded. 



Applying to atoms the mechanical law which holds of 

 masses, that since inertia and gravity increase as the cubes 

 of the dimensions while cohesion increases as their squares, 

 the self-sustaining power of a body becomes relatively 

 smaller as its bulk becomes greater ; it might be argued that 

 these large, aggregate atoms which constitute organic sub- 



