AMOEBA 133 



accompanied by a similar streaming of the internal granules 

 can be induced in droplets of various fluids in which solid 

 particles are suspended. For instance a drop of glycerine 

 impregnated with soot and immersed in oil may be made 

 to move in this manner over a piece of cardboard a portion 

 of whose surface has been wetted to prevent the oil soaking 

 into it. This experiment and others of a like nature have 

 led many people to believe that the movements of Amoebae can 

 be explained on simple chemical and physical grounds, and 

 some of the theories proposed are at least partly justified by 

 the remarkable analogies observed between the behaviour of 

 artificial mixtures and the living organism. 



There is also a striking analogy between the structure of 

 protoplasm and that of certain artificial emulsions. It can 

 be shown that in many Amoebae the cytoplasm, including both 

 ectoplasm and endoplasm, has the structure of an exceedingly 

 fine sponge-work, or rather, let us say, a foam. Imagine a 

 foam or froth composed of bubbles of extremely minute size. 

 Imagine that the skins of these bubbles are composed of 

 a somewhat denser tenacious material and that their cavities 

 are occupied, not by air, but by a fluid of less density. The 

 bubbles in the centre of the froth would be polygonal through 

 mutual pressure, and if the whole thing could be hardened 

 and cut into slices the sections of the walls of the bubbles 

 would look like a network having somewhat irregular poly- 

 gonal meshes. Such a foam may be made by mixing finely- 

 pounded common salt with thick rancid olive oil. A small 

 droplet of this mixture, placed in water and examined under 

 the microscope, exhibits a structure marvellously like that of 

 the cytoplasm of an Amoeba. It is also divisible into an 

 outer more hyaline border and an inner granular mass, and 

 it has been shown that the outer hyaline border is due to 

 the special form assumed by the alveoli or bubbles in con- 

 sequence of the surface tension produced by the contact 

 of two immiscible liquids of different densities. A similar 

 arrangement is found in the hyaline border or ectoplasm of 

 an Amoeba and it is permissible to assume that the similar 

 effects observed in the two cases are due to like causes. It 

 has further been shown that if the surface tension be reduced 

 at any point of the droplet of salt and oil a streaming 

 movement of its contained granules will be set up in the 



