434 INTRODUCTION TO CYTOLOGY 



other a more limpid fluid with granules suspended in it. De Bary 

 (1859, 1864), on the other hand, regarded protoplasm as a single semi- 

 fluid substance, contractile throughout, but showing many local differ- 

 ences due to varying water content. Probably the first man to recognize 

 the importance of the colloidal state of matter, newly distinguished by 

 Graham, in the study of protoplasm was W. Hofmeister (1862, 1867), 

 but many years were to elapse before such studies could be effectively 

 pursued. 



More influential for a time were the structural theories associated 

 with the names of Klein, Flemming, Altmann, and Blitschli, and known 

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

 theories. The reticular theory, which was formulated by Frommann 

 (1865, 1875, 1884), was developed especially by Klein (1878, 1879) 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 held a fluid and granules in its meshes. 



The fibrillar, or filar, theory announced by Velten (1873, 1876), 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 it paramitome. Some observers asserted that the fibrils 

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

 others being merely sections of these canals. 



According to the granular theory, protoplasm was a compound of innu- 

 merable minute granules which alone form the essential active basis for 

 the phenomena exhibited; the observed fibrillar and alveolar structures 

 were of secondary importance. For Altmann (1886 et seq.), who was the 

 most prominent exponent of the theory, the granules were actual elemen- 

 tary living units, or "bioblasts," the liquid containing them being a 

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

 unit but as an assemblage of bioblasts, "like bacteria in a zoogloea," 

 and the bioblasts 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 Blitschli (1892 et seq.), and is of special 

 interest in view of certain present-day notions of protoplasmic structure. 

 According to Blitschli, protoplasm consists of minute droplets (averaging 

 Ijj. in diameter) of a liquid "alveolar substance" (enchylema) suspended 

 in another continuous liquid " interalveolar substance." The structure 

 is, therefore, that of an extremely fine emulsion, and the appearances 

 described by other workers are due to optical effects encountered in 

 examining the minute alveolar structure. Blitschli supported his theory 



