PROTOPLASM 33 



1864), on the other hand, regarded protoplasm as a single semi-fluid sub- 

 stance, contractile throughout, but showing many local differences due to 

 varying water content. To this general view the work of Hanstein 

 (1870, 1880, 1882) lent support. 



Much more prominent have been the structural theories associated 

 with the names of Klein, Flemming, Altman, and Biitschli, and known 

 respectively as the "reticular," "fibrillar," "granular," and "alveolar" 

 theories. 



The reticular theory, which was formulated by Fromman (1865, 

 1876, 1884), was developed especially by Klein (1878-9) and supported 

 by van Beneden, Carnoy, Leydig, and others. These workers saw in 

 protoplasm a reticulum or fine network of a rather solid substance 

 (spongioplasm) , which holds a fluid and granules in its meshes. This 

 view was adopted for a time by Strasburger. 



The fibrillar, or filar, theory, announced by Velten (1873-6) as a 

 result of his observations on Tradescantia and other forms, stated that 

 protoplasm is composed of fine fibrils, which, though often branched, 

 do not form a continuous network. This idea was developed mainly by 

 Flemming (1882), who called the substance of the fibrils mitome and the 

 fluid bathing them paramitome. Some observers asserted that the fibrils 

 are in reality minute canals filled with a liquid, the granules seen by 

 others being merely sections of these canals. An extreme view was that 

 of Schneider (1891), who thought the entire cell might consist of but a 

 single greatly convoluted filament. 



To the followers of the reticular and fibrillar theories the fluid held 

 between the fibers was known variously as ground substance, enchylema 

 (Hanstein 1880), hyaloplasma (Hanstein), paramitome, and inter-filar 

 substance. The granules were known generally as microsomes (Hanstein). 



According to the granular theory protoplasm is a compound of in- 

 numerable minute granules which alone form the essential active basis for 

 the phenomena exhibited; the observed fibrillar and alveolar structures 

 are of secondary importance. Martin (1881) held that fibrils and net- 

 works are due entirely to certain arrangements of these granules, or 

 microsomes. Pfitzner (1883) pointed out that the granules are semi- 

 solid and float in a more fluid ground substance. For Altman (1886, etc.), 

 who was the most prominent exponent of the theory, the granules were 

 actual elementary living units, or bioplasts, the liquid containing them 

 being a non-living hyaloplasm. The cell was therefore looked upon not 

 as a unit, but as an assemblage of bioplasts, "like bacteria in a zooglcea," 

 and the bioplasts were believed to arise only by division of others of their 

 kind (omne granulum e granulo!). 



The alveolar theory, also known as the emulsion, or foam, theory, was 

 elaborated principally by Biitschli (1882, etc.), and is of special interest 

 in view of our present-day notions of protoplasmic structure. According 



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