668 ON CONCRETIONS, SPICULES, ETC. [ch. 



bubbles in chrome-gelatine, and which he usecT in one of his early 

 (and none too fortunate) speculations on the nature of the nuclear 

 spindle. 



We see that the methods by which we attempt to study the 

 chemico-physical characteristics of an inorganic concretion or spicule 

 within the body of an organism soon introduce us to a multitude 

 of phenomena of which our knowledge is extremely scanty, and 

 which we must not attempt to discuss at greater length. As regargls 

 our main point, namely the formation of spicules and other 

 elementary skeletal forms, we have seen that some of them may 

 be safely ascribed to precipitation or crystalhsation of inorganic 

 materials in ways modified by the presence of albuminous or other 

 colloid substances. The effect of these latter is found to be much 

 greater in the case of some crystalhsable bodies than in others. 

 For instance Harting, and Rainey also, found that calcium oxalate 

 was much less affected by a colloid medium than was calcium 

 carbonate; it shewed in their hands no tendency to form rounded 

 concretions or " calcospherites " in presence of a colloid, but con- 

 tinued to crystallise, either normally or with a tendency to form 

 needles or raphides. It is doubtless for this reason that, as we have 

 seen, crystals of calcium oxalate are so common in the tissues of 

 plants, while those of other calcium salts are rare; but true calco- 

 spherites, or spherocrystals, even of the oxalate are occasionally 

 found, for instance in certain Cacti, and Biitschli* has succeeded 

 in making them artificially in Harting's usual way, that is to say 

 by crystalhsation in a colloid medium. If the nature of the salt 

 has a marked specific qffect, so also has the gel: silver chromate 

 is thrown down in rings in gelatin but not in agar; replace the 

 silver by lead, and the rings come in agar but not in gelatin; while 

 neither lead nor silver produce them in silicic- acid gel. 



There link on to such observations as Harting's, and to the 

 statement already quoted that calcareous deposits are associated 

 with the dead residua, or "formed materials," rather than with 

 the living cells of the organism, certain very interesting facts in 

 regard to the solubility of salts in colloid media, which go far to 

 account for the presence (apart from the form) of calcareous pre- 



* Spharocrystalle von Kalkoxalat bei Kakteen, Ber. d. d. Bot. Gesellsch. p. 178, 

 1885. 



