420 THE LIFE OF MATTER. 



homorpliiHin and the faculty ofc7x>ssing. — Besides, the possibility, 

 in the case of isomorphous bodies, of replacing each other in the same 

 crystal during the process of formation and of thus mingling, so 

 to speak, their congenital elements, may be compared with the pos- 

 sibility of interbreeding with living beings of the same species. 

 Isomorphism is thus a kind of faculty of crossing. And as the impos- 

 sibilit}^ of crossing is the touchstone of taxonomic relationship, as it 

 is the proof of it, separating stocks that ought to be separated, so the 

 operation of crystallization is also a means of separating from an acci- 

 dental mixture of mineral species the pure forms which are there 

 blended. Crystallization is the touchstone of the specific purity of 

 minerals; and it is an important process in chemical purification. 



Other aiioloyic.s. — The analogies between cr3"stalline and living forms 

 ha^•e been pushed still further, even to the verge of abuse. 



The internal and external symmetry of animals and plants has been 

 compared to that of crystals. Transitions or intergradations have 

 been sought between the rigid and faceted architecture of the latter 

 and the flexible structure and curved surfaces of the former; the utric- 

 ular form of sublimated sulphur on the one hand and the geometrical 

 structure of the testa of radiolarians on the other are thought to show 

 an exchange of typical forms between the two systems. An effort 

 has even been made to draw a parallel between six of the principal 

 main stems of the animal kingdom and the six crystalline systems. 

 Pushed to this degree the proposition takes on a puerile character. 

 Real analogies will suffice. Among these the curious facts of crystal- 

 line lenewal deserve first place. 



'•1. CICATRIZATION IN LIVING BEINGS AND IN CRYSTALS. 



We know that living beings not only possess a typical architecture 

 that they have themselves constructed, ))ut that they defend it against 

 destructive agencies and that at need they repair it. The living- 

 organism cicatrizes its wounds, repairs losses of substance, regener- 

 ates more or less perfectly the parts tluit have been removed: in other 

 terms, when it has been mutilated it tends to reconstruct itself accord- 

 ing to the laws of its own morphology. This phenomenon of recon- 

 stitution oi- redintegration, these more or less successful efforts to 

 reestablish its form in its integrity, appear, at first sight, to be a char- 

 acteristic feature of living beings. That is not the case. 



M.utilatiooi and redintegration of eri/xtals. — Crystals — let us say 

 crystalline individuals — show a similai- aptitude for repairing their 

 mutilations. Pastcnir, in an (^arly work, discussed these curious facts. 

 Other ex])(M'iment(n's, Gernez a little liit(M" and Rauber (|uite recenth', 

 took \\\) the same subject and were only ahle to extend and confirm his 

 observations. Crystals are formed from a primitive nucleus as the 

 animal is foi-med from an Qgg\ their integral particles are disposed 



