HISTORICAL SKETCH 433 



seen a similar substance in plant-cells; in 1846 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 protoplasm 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, consist 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 meta- 

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

 manifest in movement is especially exhibited by a nitrogenous contractile sub- 

 stance, 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 (1861) was espe- 

 cially important in that it firmly established the protoplasm doctrine, 

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

 this substance is, in general, siynilar in all living organisms. Schultze 

 described the cell as a mass of protoplasm containing a nucleus, both 

 nucleus and protoplasm arising through the division of the corresponding 

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

 workers had focused their attention, turned out to be of secondary 

 importance. The cell was thus seen to be primarily the organized proto- 

 plasmic mass, to which Hanstein in 1880 applied the convenient term 

 protoplast. 



Extensive studies on the physical nature of protoplasm were soon 

 undertaken. Briicke (1861), who was one of the first to lay emphasis on 

 the fact that protoplasm is an organized substance, looked upon it as a 

 contractile, semisolid material through which there streams a fluid 

 carrying granules. Similar to this was the idea of Cienkowski (1863), 

 who believed he saw in the protoplasm of myxomycetes two fluids, one 

 of them hyaline and only semifluid (the "ground substance"), and the 



