CHAP. II.] ANORGANIC AND ORGANIC SUBSTANCES., 17 



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There is not, however, any absolute i ncompatibili ty between 

 colloids and crystalloids. If the colloids are for the most part 

 complex organic compositions, we have seen above that very 

 simple mineral compounds can assume the colloidal state ; and 

 on the other hand Reichert discovered in 1849 that albumino idal 

 substances can take the crystalloidal form. We shall be able 

 to cite examples of. this last case when speaking of plants. In 

 almost all seeds, in efiect, we find a white powder, finely grained, 

 and presenting sometimes crystallised facets, square edged. 

 The diameter of these particles is from 0",00125 to 0",0375. 

 They are called particles of aleurone. They are composed oi 

 fibrins, of albumine, of legumine, of gliadine, of gum, of sugar, 

 and so on. They are aliments in reserve. 



These albuminoidal crystalloids are birefringent ; they are all 

 insoluble and unassailable in water and alcohol.^ 



We have signalised above the strong difiusibility of the crys- 

 talloids ; it is so great that they can penetrate the colloids, 

 blend with them as intensely as with water, while on the con 

 trary the colloids can scarcely diffuse themselves into effective 

 union with each other. 



From this enormous difference of difiusibility between colloids 

 and crystalloids it results that, if we separate by a porous mem- 

 brane water and a colloid holding in solution a crystalloid, this 

 last disengages itself from the colloid and traverses the mem- 

 brane to dissolve in the water. It is thus that we can very 

 easily with a membrane dialyser extract from a colloidal substance 

 arsenious acid, digitaline, and so on. This process is made use ol 

 in certain toxicological researches, and also industrially to purify 

 gums, albumine, caramel, and the like. 



The reader has no doubt already the presentiment of the 

 weight and worth of some preceding statements for the compre 

 hension of biological facts. In effect every organised being is a 

 compound of colloidal bodies holding in solution crystalloidal 

 bodies. But this organised body is in a state of perpetual reno- 

 1 Duehai-tre, BotaniqiM, p. 69 ; Sachs, TraiU de Botcmique, p. 72. 



