18 Causes and Course of Organic Evolution 



particles, the latter appear as a very fine liquid emulsion; the 

 former become coagulated and precipitated when any electro- 

 lytic substance is added to the solution, the latter are not 

 coagulated by small quantities of electrolytes, but they can 

 be coagulated by large amounts of neutral salts; the former 

 are highly mobile, the latter viscous and inclining readily 

 to gelatinize. The above precipitation action is evidently due 

 to the comparatively large colloid molecules falling together 

 into larger aggregates of greater density. 



As to the possible relation of these two to each other, results 

 have been obtained that are highly suggestive for living tissues. 

 Thus if traces of the emulsoid gelatine be placed in a gold 

 solution, and an electrolyte be then added, the gelatine pre- 

 vents precipitation of the gold particles by apparently forming 

 a protective coat round the latter, that shields these from 

 electrolytic action. 



Added features of interest from the standpoint of organic 

 bodies are, that the molecular weight of colloids is always 

 higher, often greatly higher, than that of crystalloids; and 

 that, while crystalloids can diffuse themselves through colloids 

 nearly as rapidly as through water, colloids can scarcely diffuse 

 at all through other colloids. "So we must regard the colloid 

 compounds of which organisms are built as having, by their 

 physical nature, the ability to separate colloids from crystal- 

 loids, and let crystalloids pass through them with scarcely 

 any resistance/' Graham further pointed out that even the 

 colloid body, if made up of constituents that are of feeble 

 affinity, may undergo splitting up if passed through a dialyzer. 

 Thus the hydrochloride of sesquioxide of iron (Fe2Cl6H240i2) 

 separates into hydrochloric acid and the colloid sesquioxide of 

 iron. 



Again attention has been drawn to the similarity in action 

 of some inorganic colloids to the organic ferments. Thus the 

 dark brown liquid that is the colloid state of platinum has been 

 found by Bredig and Von Berneck to decompose "hydrogen 

 dioxide like organic ferments, and resembles the latter in many 

 other particulars. A gram atomic weight of platinum in 



