LIVING SUBSTANCE 



85 



I. The Gmond-substance of Protoplasm 



As already noted, the ground-substance of protoplasm, in which 

 the granules, etc., are embedded, appears upon superficial examina- 

 tion completeh- homogeneous. This can be seen best in cells that 

 contain onl}- a few solid constituents stored in their ground - 

 substance ; it is especially evident in many Amaibm, which are 

 free-living cells possessing naked protoplasmic bodies that creep 

 about at the bottom of stagnant water, constantly changing their 

 form, and represent the lowest and simplest organisms inhabiting 

 the surface of the earth. These interesting elementary organisms 

 usually form upon their surface pseudopodia which are wholly free 

 from granules, broad, finger-shaped, or lobate, and appear com- 

 pletely hyaline and structureless (Fig. 16, p. 75, and Fig. 28). In 

 fact, in the Amcehm the hyaline protoplasm not rarely is completely 

 structureless. All investigations up to the 

 present time which have been undertaken 

 with the best microscopic methods agree in 

 this. 



But this actual homogeneity of the ground- 

 substance of protoplasm is not the rule ; on 

 the contrary, the employment of high magni- 

 fying powers shows that by far the majority 

 of cells possess in reality in their apparently 

 homogeneous ground-mass an extremely fine 

 and characteristic structure. 



Remak ('44) observed that not only nerve- 

 fibres but also the ganglion-cells of the central 

 nervous system possess a very fine fibrous or 

 fibrillar structure — an observation that was 

 confirmed and extended by a large number of 

 investigators, especially by Max Schultze (71). 

 A striated structure was later found in the 

 protoplasm of various other cells, gland-cells, 

 epithelium-cells, muscle-cells, etc., and thus 

 the idea was formed by various investigators that a fibrillar struc- 

 ture is wide-spread in protoplasm ; this view is still defended to- 

 day, especially by Flemming, Ballowitz, and Camillo Schneider. 



But this theory earl}- underwent a modification. Beginning in 

 1867, Frommann especially endeavoured to show by a long series 

 of researches that the finer structure of the protoplasm of all cells 

 is not properly fibrillar, but reticular ; this view was adopted 

 almost at the same time by Heitzmann, and soon obtained wide 

 acceptance. According to this idea, protoplasm forms a network, 

 or, better, a meshwork, the nodal points of which appear as indi- 

 vidual granules. The whole meshwork of the cell is open to the 



FiQ. 28.— An amceba-cell 

 containing completely 

 hyaline and homogene- 

 ous pseudopodial pro- 

 toplasm. In the endo- 

 plasm by the side of the 

 nucleus lies a pale con- 

 tractile vacuole (droplet 

 of liquid). 



