V] OF CRYSTALLINE AND COLLOID BODIES 203 



to follow, must occur symmetrically. Our piling up of shot, or 

 manufacture of mimic crystals, gives us visible demonstration 

 that the result is actually to obtain, as in the natural crystal, 

 plane surfaces and sharp angles, symmetrically disposed. 



But the living cell grows in a totally dift'erent way, very much 

 as a piece of glue swells up in water, by "imbibition," or by inter- 

 penetration into and throughout its entire substance. The semi- 

 fluid colloid mass takes up water, partly to combine chemically 

 with its individual molecules*, partly by physical diffusion into 

 the interstices between these molecules, and partly, as it would 

 seem, in other ways ; so that the entire phenomenon is a very 

 complex and even an obscure one. But, so far as we are con- 

 cerned, the net result is a very simple one. For the equilibrium or 

 tendency to equilibrium of fluid pressure in all parts of its interior 

 while the process of imbibition is going on, the constant rearrange- 

 ment of its fluid mass, the contrast in short with the crystalline 

 method of growth where each particle comes to rest to move 

 (relatively to the whole) no more, lead the mass of jelly to swell 

 up, very much as a bladder into which we blow air, and so, by 

 a graded and harmonious distribution of forces, to assume every- 

 where a rounded and more or less bubble-like external formf. 

 So, when the same school of older naturahsts called attention to 

 a new distinction or contrast of form between the organic and 

 inorganic objects, in that the contours of the former tended to 

 roundness and curvature, and those of the latter to be bounded 

 by straight lines, planes and sharp angles, we see that this contrast 

 was not a new and different one, but only another aspect of 

 their former statement, and an immediate consequence of the 

 difference between the processes of agglutination and intussus- 

 ception. 



This common and general contrast between the form of the 

 crystal on the one hand, and of the' colloid or of the organism on 

 the other, must by no means be pressed too far. For Lehmann, 



* This is what Graham called the water of gelatination, on the analogy of xvater 

 of crystallisation ; Chem. and Phys. Researches, p. 597. 



f Here, in a non-crystalline or random arrangement of particles, symmetry 

 ensures that the potential energy shall be the same per unit area of all surfaces; 

 and it follows from geometrical considerations that the total surface energy will 

 be least if the surface be spherical. 



