34 INTRODUCTION TO CYTOLOGY 



to Butschli protoplasm consists of minute droplets (averaging 1/* 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. Butschli supported his theory 

 by making artificial emulsions with soaps and oils which showed amoeboid 

 movement and other striking resemblances to living protoplasm. 



The above four theories have been termed "monomorphic theories," 

 for the reason that each of them stated that protoplasm has a single 

 characteristic physical structure. Strasburger in 1892 and thereafter 

 maintained that the protoplast is regularly composed of two portions; 

 an active fibrillar kinoplasm, concerned primarily with the motor work of 

 the cell, and a less active alveolar trophoplas?n, chiefly nutritive in func- 

 tion. It was shown by von Kolliker, Unna (1895), and others, moreover, 

 that one type of structure may be transformed into another. Flemming 

 later adopted the view that no single type characterizes protoplasm, but 

 that the latter may be homogeneous, alveolar, fibrillar, or granular — 

 i.e., it is " polymorphic." Wilson (1899) found that all four states are 

 successively passed through in the echinoderm egg. This observation, 

 which was made upon both living and fixed material, showed in a striking 

 manner the colloidal nature of protoplasm (see below), since it is now 

 known that colloids may assume very diverse structures under the in- 

 fluence of changing environmental conditions. The work of A. Fischer 

 (1899), who treated non-living proteins with cytological fixing reagents 

 and so produced artifacts similar to alveolae, reticula, and granules, should 

 make one cautious in drawing conclusions regarding protoplasmic 

 structure from fixed material. It should be understood that the only 

 trustworthy observations are those which are made at least in part on 

 living material, for it is not difficult to discover all four types of struc- 

 ture in prepared slides: the protoplasm has there been coagulated by 

 fixing reagents, and we know that in the coagulation of such substances 

 as compose protoplasm an entirely new structure may be assumed. 



Protoplasm as a Colloidal System. — For adequate reasons it is now 

 customary to speak of protoplasm in terms of the physics and chemistry 

 of colloids. Colloids are those glue-like substances which are uncrystal- 

 line, semi-solid, and very slightly or not at all osmotic. They have a 

 high surface tension, coagulate readily, and conduct the electric current 

 very poorly. They are " disperse heterogeneous sytems, i.e., they consist 

 essentially of particles larger than molecules of a substance or substances 

 in a medium of dispersion which may be water or some other fluid ' ; 

 (Child 1915 1 ). The particles range in size from those visible to the naked 



1 These paragraphs on colloids are based largely upon the convenient summary 

 given by Child (1915, pp. 20 ff.). See also Czapek (19116), Baylies (1915), Hatschek 

 (1916), Bechhold (1919), and Robertson (1920). 



