GENERAL PHYSICAL CONSTITUTION OF LIVING MATTER 33 



or oil. Soap solution diminishes the surface tension between water and 

 oil. The question arises as to how this circumstance can make the 

 emulsion more durable. The answer is as follows: If a film of water 

 separates two oil drops, the soap particles gather at the surface on 

 either side of the water film. If these soap particles be now brushed 

 aside on one spot of this watery film, the water will come in direct con- 

 tact with the oil. The surface tension between oil and water is greater 

 than that between soap solution and water. Hence, in a spot where 

 the soap is removed the surface tension or tendency to contract will 

 be greater than in the rest of the film, and the consequence will be that 

 this spot will contract and thus mend the hole in the layer of soap. In 

 this way the diminution of the surface tension by the contaminating 

 substance makes the emulsion more durable, and prevents the fusion 

 of two neighboring droplets in an emulsion. It is not impossible that 

 the existence of such a film may explain why it is that the cleavage cells 

 of an egg do not easily fuse. 



As far as the thickness of the contaminating layer is concerned, 

 Lord Rayleigh has measured it, and found that the contaminating 

 layer of oil on the surface of water which suffices to prevent the motion 

 of particles of camphor on the surface of water, need be only Yg^VoTro 

 mm. thick. It is hardly necessary to mention that such a film is far 

 below the limits of microscopic visibility. 



Biitschli assumes that living protoplasm is an emulsion of two 

 liquids : a viscous one, which is insoluble in water ; and a watery liquid, 

 which possesses little viscosity.* 



3. THE COLLOIDAL CHARACTER OF LIVING MATTER 



Hardy as well as Biitschli assumes that living matter is essentially 

 liquid. The most common observations on living organisms, which 

 are sufficiently transparent, show that this is undoubtedly true for a 

 large part of the material contained in such organisms. Certain ele- 

 ments, however, are apparently solid, e.g. the surface films of cells and 

 nuclei, and possibly certain structures in the interior of the cell, such 

 as centrosomes. The observations of Traube, as well as Hardy, show 

 how solid constituents can be formed from liquids in living matter. 

 We are dealing here with a chapter of the physics of colloids, which 

 is just at present the object of many investigations. 



The substances in living matter which occur in a liquid as well as 

 in a solid condition are the colloids. The name was given by Graham, 

 who discriminated between two kinds of soluble substances, crystal- 



* Butschli, Archiv fur Entwickelnngsmechanik, Vol. II, 499, 1901. 

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