86 GENERAL PHYSIOLOGY 



outside, and between its threads exists a liquid, which, however, is 

 different from the liquid of the medium in which the cell lives, i.e., 

 the water, the body-juices, etc. It is difficult to understand why, 

 as the adherents of the theory of the reticular structure of pro- 

 toplasm hold to be possible, the internal cell-liquid in cells that 

 possess no membrane, such as the leucocytes of the blood and 

 Amoeba, the reticular structure of which has been described by 

 Heitzmann in great detail, does not continually mix with the sur- 

 rounding medium in spite of its great proportion of water. But 

 attempts to stain such living protoplasmic masses by certain 

 staining-solutions show clearly that the staining-fluid does not 

 penetrate into the living protoplasm. This and similar difficulties 

 which arise in connection with the idea of protoplasm as a mesh- 

 work open upon all sides have led many investigators to take a 

 very sceptical attitude toward the theory of a reticular structure, 

 although in various ways the reticular appearance of the protoplasm 

 of many cells has been confirmed. 



The striking researches with which in recent years Biitschli 

 ('92, 1) has been surprising the scientific world, have completely 

 clarified our ideas upon the real nature of the protoplasmic struc- 

 tures so much observed. The protoplasm of a cell that contains 

 so many vacuoles or droplets of liquid that its contents have a 

 foamy appearance, presents with high powers of the microscope a 

 picture, not of many vacuoles or bubbles pressed tightly together, 

 but of a network, the threads of which form the cross-sections of 

 the thin walls of the vacuoles. This is due to the fact that with 

 strong powers surfaces only, and never bodies, are seen. The 

 microscope shows only optical cross-sections of bodies. But the 

 optical cross-section of a foam is a network. This fact led Biitschli 

 to the conviction that the finer reticular appearance of protoplasm 

 which appears homogeneous by feeble magnification, as has been 

 observed in so many cells, is merely the optical expression of an 

 extremely finely vacuolated foam-structure. In order to confirm 

 this idea, Btitschli endeavoured artificially to produce microscopic 

 foams of a fineness equal to the hypothetical protoplasmic struc- 

 tures, and he succeeded in this in a most gratifying manner. He 

 employed for his experiments oil which was very finely rubbed up 

 with potash or cane-sugar. Small droplets of this oil-mixture, 

 when placed upon a slide with a drop of water, covered with a 

 cover glass, and observed under a microscope, immediately took on 

 an extremely fine foam-structure. This was due to the fact that 

 the particles of potash or sugar, which were finely divided in the 

 oil-droplet, attracted particles of water ; the latter passed from the 

 outside through the oil by diffusion, accumulated as extremely fine 

 droplets closely about the former, and transformed the oil into a 

 very fine foam. The oil-foams obtained in this way show such a 

 remarkable similarity to the structure of protoplasm that they can 



