HISTORICAL SKETCH 11 



The Protoplasm Doctrine. The Cell Theory and all of its corollaries 

 were placed in a new light with the development of a more adequate 

 conception of the significance of protoplasm. To its discoverers the 

 cell meant nothing more than the wall surrounding a cavity; they spoke 

 only in the vaguest terms of the "juices" present in cellular structures. 

 The founders of the Cell Theory held a position but little in advance of 

 this; they observed the cell contents but regarded them as of relatively 

 slight importance. Even those who had been impressed by the phe- 

 nomenon of protoplasmic streaming were not aware of the significance of 

 the substance before their eyes. 



Felix Dujardin (1801-1860) in 1835 described the "sarcode" of the 

 lower animals as a substance having the properties of life. Von Mohl 

 had seen a similar substance in plant cells, and in 1846, as noted above, 

 he called it "Schleim," or "Protoplasma," the latter term having been 

 used shortly before by Purkinje in a somewhat different sense. Nageli 

 and A. Payen (1795-1871) in 1846 recognized the importance of proto- 

 plasm as the vehicle of the vital activity of the cell ; and Alexander Braun 

 (1805-1877) in 1850 pointed out that swarm spores, which are cells, con- 

 sist of naked protoplasm. An important point was reached when Payen 

 (1846) and Ferdinand Cohn (1850) concluded that the "sarcode" of 

 the animal and the "protoplasm" of the plant are essentially similar 

 substances. In the words of Cohn: 



"The protoplasm of the botanist, and the contractile substance and sarcode 

 of the zoologist, must be, if not identical, yet in a high degree analogous sub- 

 stances. Hence, from this point of view, the difference between animals and 

 plants consists in this ; that, in the latter, the contractile substance, as a primordial 

 utricle, is enclosed within an inert cellulose membrane, which permits it only to 

 exhibit an internal motion, expressed by the phenomena of rotation and circula- 

 tion, while, in the former, it is not so enclosed. The protoplasm in the form 

 of the primordial utricle is, as it were, the animal element in the plant, but which 

 is imprisoned, and only becomes free in the animal; or, to strip off the metaphor 

 which obscures simple thought, the energy of organic vitality which is manifested 

 in movement is especially exhibited by a nitrogenous contractile substance, which 

 in plants is limited and fettered by an inert membrane, in animals not so." 



Protoplasm was now studied more intensively than ever. H. A. 

 de Bary (1831-1888), working on myxomycetes and other plant forms, 

 and Max Schultze (1825-1874), investigating animal cells, demonstrated 

 the correctness of Cohn's view. The work of Schultze was especially 

 important in that it firmly established in 1861 the Protoplasm Doctrine, 

 namely, that the units of organization are masses of protoplasm, and that 

 this substance is essentially similar in all living organisms. The cell, 

 according to Schultze, is "a mass of protoplasm containing a nucleus, 

 both nucleus and protoplasm arising through the division of the corres- 

 ponding elements of a preexisting cell." The cell wall, upon which the 



