IX] AND SPICULAR SKELETONS 649 



in the presence of excess of lime their shells become much altered, 

 are strengthened with various ridges or "ornaments," and come to 

 resemble other varieties and even "species*." 



The crucial experiment, then, is to attempt the formation of 

 similar spicules or concretions apart from the living organism. But 

 however feasible the attempt may be in theory, we must be prepared 

 to encounter many difficulties; and to realise that, though the 

 reactions involved may be well within the range of physical chemistry, 

 yet the actual conditions of the case may be so complex, subtle and 

 dehcate that only now and then, and only in the simplest of cases, 

 has it been found possible to imitate the natural objects successfully. 

 Such an attempt is part of that wide field of enquiry through which 

 Stephane Leduc and other workers have sought to produce, by 

 synthetic means, forms similar to those of living things; but it is 

 a circumscribed and well-defined part of that wider investigationf. 



When we find ourselves investigating the forms assumed by 

 chemical compounds under the pecuhar circumstances of association 

 with a Hving body, and when we find these forms to be characteristic 

 or recognisable, and somehow different from those which the same 

 substance is wont to assume under other circumstances, an analogy, 

 captivating though perhaps remote, presents itself to our minds 

 between this subject of ours and certain synthetic problems of the 

 organic chemist. There is doubtless an essential difference, as well 

 as a difference of scale, between the visible form of a spicule or con- 



* Cf. Heron-Allen, Phil. Trans. (B), ccvi, p. 262, 1915. 



f Leduc's artificial growths were mostly obtained by introducing salts of the 

 heavy metals or alkaline earths into solutions which form with them a "precipitation- 

 membrane" — as when we introduce copper sulphate into a ferrocyanide solution. 

 See his Mechanism of Life, 1911, ch. x, for copious references to other works on 

 the "artificial production of organic forms." Closely related to Leduc's experi- 

 ments are those of Denis Monnier and Carl Vogt, Sur la fabrication artificielle 

 des formes des elements organiques, Journ. de VAnaf. xviii, pp. 117-123, 1882; 

 cf. Moritz Traube, Zur Geschichte der mechanischen Theorie des Wachstums der 

 organischen Zelle, Botan. Ztg. xxxvi, 1878. Cf. also A. L. Herrera, Sur les 

 phenomenes de vie apparente observes dans les emulsions de carbonate de chaux 

 dans la silice gelatineuse, Mem. Soc. Alzaje, Mexico, xxvi, 1908; Los Protobios, 

 Boll, de la Dir. de Estud. Biolog., Mexico, i, pp. 607-631, and other papers. Also 

 {int. al.) R. S. Lillie and E. N. Johnston, Precipitation-structures simulating organic 

 growth, Biol. Bull, xxxiii, p. 135, 1917; xxxvi, pp. 225-272, 1919; Scientific 

 Monthly, Feb. 1922, p. 125; H. W. Morse, C. H. Warren and J. D. H. Donnay, 

 Artificial spherulites, etc., Ainer. .11. of Sci. (5) xxiii, pp. 421-439, 1932. 



