STRUCTURES RESEMBLING ORGANIC GROWTHS. 137 



any kind of activity involving breakdown of material, a process 

 of chemical and structural reconstitution or reorganization takes 

 place, and that in this process electrical factors play an important 

 part. 1 Finally it should be noted that the physiological effects 

 at anode and cathode are typically contrasted in a manner which 

 inevitably recalls the contrast between the two electrodes in 

 electrolysis; and while this resemblance does not prove that 

 processes of electrolysis enter in producing the physiological 

 effect since the current may have other kinds of polar action- 

 it undoubtedly favors such an interpretation. 



The similarity of certain types of electrolytic deposit to vege- 

 tative growths has long attracted the attention of chemists. 

 This is especially the case with the so-called lead-trees, tin- 

 trees, etc., obtained when salts of these metals undergo spon- 

 taneous electrolysis in contact with baser metals; thus when a 

 piece of zinc is suspended in a solution of tin chloride or lead 

 acetate the metal of the salt is deposited upon the zinc in a 

 tree-like branching form; this metallic deposit grows outward 

 through the solution because each portion of metal as deposited 

 forms a cathodic surface which itself becomes the site of a 

 chemical change similar to that at the original surface of dep- 

 osition. An analogy to organic growth is evident here; in 

 both processes certain substances are selectively removed from 

 solution, chemically transformed, and deposited to form a 

 definite type of structure. A further resemblance between such 

 a process of electrolytic accretion and true organic growth is 

 that in electrolysis material may be deposited from solutions of 

 all degrees of concentration. In this respect the extension of a 

 metallic cathode in a solution of its salt presents a closer analogy 

 to organic growth than does the increase in size of a crystal in a 

 supersaturated solution, since in organic growth the abstraction 

 of food-substances from solution and their transformation into 

 structural material or living protoplasm may also take place 

 from very dilute solution. 



Structures having a remarkably close superficial resemblance 

 to plant growths and other cell-structures are also formed under 

 certain conditions (partly described below) from metals under- 



1 Cf. my recent paper in Amer. Journ. Physiol., 1917, Vol. 43, p. 43; see pp. 56-7. 



