658 ON CONCRETIONS, SPICULES, ETC. [en. 



the same agency the coarser particles are in turn agglutinated into 

 visible lumps; and the form of the calcospherites, whether it be 

 that of the solitary spheres or that assumed in various stages of 

 aggregation (e.g. Fig. 300)*, is hkewise due to the same agency. 



From the point of view of colloid chemistry the whole pheno- 

 menon is important and significant; and not the least significant 

 part is this tendency of the solidified deposits to assume the form 

 of "spheruhtes" and other rounded contours. In the phraseology 



Fig. 299. A "crust" of close-packed 



calcareous concretions, precipitated Fig. 300. Aggregated calco- 



at the surface of an albuminous spherites. After Harting. 



solution. After Harting. 



of that science, we are dealing with a iwo-phase system, which 

 finally consists df solid particles in suspension in a liquid — a disperse 

 phase ir^ a dispersion medium. In accordance with a rule first 

 recognised by Ostwald, when a substance begins to separate out 

 from a solution, so making its appearance as a new phase, it always 

 makes its appearance first as a liquid f. Here is a case in point. 

 The minute quantities of material, on th^ir way from a state of 

 solution to a state of "suspension," pass through a Hquid to a sohd 

 form; their temporary sojourn in the former leaves its impress in 

 the rounded contours which surface-tension brought about while the 

 httle aggregate was still labile or fluid : while coincidently with this 

 surface-tension effect, crystallisation tends to take place throughout 

 the httle liquid mass, or in such portions of it as have not yet con- 

 solidated and crystallised. 



* The artificial concretion represented in Fig. 300 is identical in appearance 

 with the concretions found in the kidney oi Nautilus, as figured by Willey (Zoological 

 Results, p. Ixxvi, Fig. 2, 1902). 



t This rule, undreamed of by Errera, supports and justifies his cardinal 

 assumption (of which we have had so much to say in discussing the forms of cells 

 and tissues) that the incipient cell-wall behaves as, and indeed actually is, a liquid 

 film (cf. p. 482). 



