CONDITION OF AGGREGATION OF ORGANISED STRUCTURES. 673 



or barium nitrate, but permeable to potassium chloride or water. Traube considers 

 that in the permeability of the pellicle-precipitates we have a means of determining the 

 relative size of the molecules of different solutions, since only those molecules can pass 

 through the pellicle which are smaller than its micellar interstices and therefore smaller 

 than the molecules of the solutions which produce it. 



If a small quantity of ammonium sulphate is added to a solution of /3 gelatine, and a 

 small quantity of barium chloride to one of tannic acid, and the two mixtures thus 

 obtained are themselves mixed, a pellicle is formed of gelatine tannate, and in it a 

 precipitate of barium sulphate which diminishes the size of the interstices; the two 

 solutions which cause the deposit can no longer diffuse ; but the incrusted pellicle is still 

 permeable to the smaller molecules of ammonium chloride and water. 



Traube maintains that there is no such thing as an endosmotic equivalent in the 

 sense of the older theory. Endosmose is independent of any interchange, since it 

 results entirely from the attraction of the soluble substance for the solvent ; and this 

 attraction is invariable at any given temperature and may be termed Endosmotic Force. 

 The endosmotic force of grape-sugar, for instance, is very great, that of gelatinous 

 substances very small. 



To these researches, which are of extreme importance in reference to vegetable 

 physiology, and of which we shall make much use in the sequel, though with a cautious 

 selection, Traube has added observations on the growth of the pellicle-precipitates of 

 copper ferro-cyanide, the main results of which however I have been unable to confirm 

 after a number of experiments. 



If a drop of a very concentrated solution of copper chloride is dropped into a 

 dilute solution of potassium ferrocyanide, it immediately becomes coated with a thin 

 brownish pellicle of copper ferrocyanide which exhibits peculiar phenomena. It is 

 more convenient to place small pieces of copper chloride in the ferrocyanide solution, 

 where a green drop is immediately formed at the expense of the water of the solu- 

 tion, producing the pellicle on its surface, and still enclosing the solid copper chloride 

 which dissolves gradually from the permeation of the water. These cells manifest active 

 growth and a variety of differences not easy to explain and dependent on secondary 

 circumstances. Some have very thin pellicles, are roundish, and exhibit a slight tendency 

 to grow upwards ; they usually form a number of small wart-like outgrowths and attain 

 very considerable dimensions (from i to 2 cm. in diameter) ; they appear to be formed 

 chiefly by the solution of large pieces of the copper chloride. Others have thick reddish 

 brown pellicles, grow quickly upwards in the form of irregular cylinders, rarely branch, 

 and attain a diameter of from 2 to 4 mm. and often a height of several centimetres. 

 Combinations of the two forms also occur which sometimes form a kind of horizontal 

 tuberous rhizome-like structure from which long stalk-like outgrowths arise upwards, 

 and root-like protuberances downwards. 



It is impossible, in the space at our disposal here, to give a detailed description 

 of these phenomena ; one only may be specially mentioned : — that these pellicles of 

 copper ferrocyanide do not grow, as Traube supposes, by intussusception, but in quite 

 a different way (by eruption). When a brown pellicle has been formed round the green 

 drops, water penetrates quickly from without through it to the copper chloride ; 

 the pellicle becomes rapidly stretched, and, as may be clearly seen, at length ruptured. 

 The green solution immediately escapes through the fissure, but becomes at once coated 

 with a pellicular precipitate which appears either as an intercalated piece of the previous 

 one, or as an excrescence or branch of it, a process which is repeated as long as any 

 copper chloride remains inside the cell. We cannot therefore in this case conclude 

 that deposition of fresh micellae of the pellicle takes place between those already in 

 existence. These cells cannot, so to speak, be injured; if they are pricked, then at 

 the moment when the point which pricks them is withdrawn an outgrowth follows 

 immediately, which is easily to be explained from what has been said. In conse- 

 quence of the rapid flowing in of water through the perforation, the dissolved or the 



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