268 CLASSICS OF MODERN SCIENCE 



We observed another law attending the development of the plastic 

 phenomena in the cells, viz. that a more concentrated solution is re- 

 quisite for the first formation of a cell than for its growth when al- 

 ready formed, a law upon which the difference between organized and 

 unorganized tissues is based. In ordinary crystallization the solution 

 must be more than saturated for the process to begin. But when it is 

 over, there remains a mother lye, according to Thenard, which is no 

 longer saturated at the same temperature. This phenomenon accords 

 precisely with the cells ; it shows that a more concentrated solution is 

 requisite for the commencement of crystallization than for the increase 

 of a crystal already formed. The fact has indeed been disputed by 

 Thomson; but if, in the undisputed experiment quoted above, the 

 crystal of sulphate of soda attracts the dissolved sulphate of soda 

 rather than the dissolved nitre, and vice versa, the crystal of nitre at- 

 tracts the dissolved nitre more than the dissolved sulphate of soda, it 

 follows that a crystal does attract a salt held in solution, because the 

 experiment proves that there are degrees of this attraction. But if 

 there be such an attraction exerted by a crystal, then the introduction 

 of a crystal into a solution of a salt, affords an efficient cause for the 

 deposition of this salt, which does not exist when no crystal is intro- 

 duced. The solution must therefore be more concentrated in the 

 latter case than in the former, though the difference be so slight as 

 not to be demonstrable by experiment. It would not, however, be 

 superfluous to repeat the experiments. In the instance of crystals 

 capable of imbibition, this difference may be considerably augmented, 

 since the attraction of molecules may increase perhaps considerably by 

 the penetrating of the solution between those already deposited. 



We see then how all the plastic phenomena in the cells may be com- 

 pared with phenomena which, in accordance with the ordinary laws 

 of crystallization, would probably appear if bodies capable of imbibi- 

 tion could be brought to crystallize. So long as the object of such a 

 comparison were merely to render the representation of the process by 

 which cells are formed more clear, there could not be much urged 

 against it; it involves nothing hypothetical, since it contains no ex- 

 planation ; no assertion is made that the fundamental power of the cells 

 really has something in common with the power by which crystals are 

 formed. We have, indeed, compared the growth of organisms with 

 crystallization, in so far as in both cases solid substances are deposited 



