142 RALPH S. LILLIE. 



precipitate unite as they separate out to form coarser aggregates 

 of relatively slight coherence; while in its presence each particle 

 of precipitate is apparently at once coated with an adsorbed 

 film of modified protein which serves to bind the particles 

 together and favors the formation of delicate and regular struc- 

 tures. In organisms the deposition of inorganic precipitates like 

 calcium carbonate or phosphate in the formation of skeletal 

 structures (bone, shell, etc.) takes place under essentially similar 

 conditions; the particles are thus deposited in finely divided 

 form, and their arrangement to form definite and regular struc- 

 tures is facilitated. This influence of albumin or gelatine upon 

 the character of precipitation-membranes and similar structures 

 has been investigated by Quincke ; J he also finds that the colloid 

 modifies very essentially the character of the structures formed. 



A certain minimal concentration of K 3 FeCy 6 is also necessary 

 for the formation of coherent filaments. In lower concentra- 

 tions the precipitate tends to separate out in non-coherent form, 

 producing irregular or amorphous deposits. Thus in experi- 

 ments with iron nails placed in a series of solutions containing 

 2 per cent, egg-albumin and I per cent. NaCl, with varying 

 concentrations of K 3 FeCy 6 , it was found that while from a 0.8 

 per cent, solution of K 3 FeCy 6 the precipitate separated chiefly 

 in filamentous form, from a 0.4 per cent, solution it was deposited 

 only in small part as filaments but chiefly as an amorphous 

 mass; in 0.2 per cent, very few filaments were formed, and none 

 in more dilute solutions. The same general result was found 

 in a second similar series with a lower concentration of NaCl 

 (1/8 per cent.). Similarly while zinc readily forms filaments in 

 an albumin solution containing 0.25 per cent. K 3 FeCy 6 , in a 

 0.13 per cent, solution only a few filaments are formed. In 

 order that coherent structures should be formed the concentra- 

 tion of soluble membrane-forming salt must exceed a certain 

 well-defined minimum. 



Structure and Manner of Formation of Filaments. The precise 

 structure of the filaments varies according to the nature of the 

 metal, the presence or absence of protective colloids, and the 

 concentration of the ferricyanide and other salts present. The 



1 Quincke: Annalen d. Physik, 1902, 4te F., Vol. 7, p. 646. 



