V] OF INTUSSUSCEPTION 349 



But the living cell grows in a totally different 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 molecules or micellae, and partly, as it would 

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

 and even an obscure onef. But, so far as we are concerned, the 

 net result is very simple. 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 rearrangement of its 

 fluid mass, the contrast in short with the crystalhne 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 everywhere a rounded and more 

 or less bubble-hke external form J. So, when the same school of 

 older naturahsts called attention to a new distinction or contrast of 

 form between 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 con- 

 sequence of the difference between the processes of agglutination 

 and intussusception §. 



So far then as growth goes on undisturbed by pressure or other 

 external force, the fluidity of the protoplasm, its mobility internal 



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

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



t On this important phenomenon, see J. R. Katz, Oesetze der Quellung, Dresden, 

 1916. Swelling is due to "concentrated solution," and is accompanied by increase 

 of volume and liberation of energy, as when the Egyptians split granite by the 

 swelling of wood. 



X 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. 



§ Intussusception has its shades of meaning; it is excluded from the idea of a 

 crystalline body, but not limited to the ordinary conception of a colloid one. When 

 new micellar strands become interwoven in the micro-structure of a cellulose cell- 

 wall, that is a special kind of "intussusception." 



