THE HISTORY OF THE PROTOPLASMIC THEORY 7 



cell, which could not be reconciled with the old conception of the 

 cell. A few years after the enunciation of Schwann's theory, 

 various investigators, Kolliker (I. 14), Bischoff (I. 4), observed 

 many animal cells, in ivliich no distinct membrane could be dis- 

 covered, and in consequence a lengthy dispute arose as to whether 

 these bodies were really without membranes, and hence not cells, 

 or whether they were true cells. Further, movements similar to 

 those seen in plant protoplasm were discovered in the granular 

 ground substance of certain animal cells, such as the lymph cor- 

 puscles (Siebold, Kolliker, Remak, Lieberkiihn, etc.). In con- 

 sequence Remak (I. 25, 26) applied the term protoplasm, which 

 Mohl had already made use of for plant cells, to the ground 

 substance of animal cells. 



Important insight into the nature of protoplasm was afforded 

 by the study of the lowest organisms, Rhizopoda (Amoebae), 

 Myxomycetes, etc. Dujardin had called the slimy, granular, 

 contractile substance of which they are composed Sarcode. Sub- 

 sequently, Max Schultze (I. 29) and de Bary (I. 2) proved, after / 

 most careful investigation, that the protoplasm of plants and i 

 animals and the sarcode of the loivest organisms are identical. 



In consequence of these discoveries, investigators, such as 

 Nageli, Alexander Braun, Leydig, Kolliker, Cohn, de Bary, etc., 

 considered the cell membrane to be of but minor importance in com- 

 parison to its contents ; however, the credit is due to Max Schultze, 

 above all others, of having made use of these later discoveries in 

 subjecting the cell theory of Schleiden and Schwann to a search- 

 ing critical examination, and of founding a protoplasmic theory. 

 He attacked the former articles of belief, which it was necessary 

 to renounce, in four excellent though short papers, the first of 

 which was published in the year 1860. He based his theory that 

 the cell-membrane is not an essential part of the elementary 

 organisms of plants and animals on the following three facts : 

 first, that a certain substance, the .protoplasm of plants and 

 animals, and the sarcode of the simplest forms, which may be 

 recognised by its peculiar phenomena of movement, is found in 

 all organisms ; secondly, that although as a rule the protoplasm 

 of plants is surrounded by a special firm membrane, yet under 

 certain conditions it is able to become divested of this membrane, 

 and to swim about in water as in the case of naked swarm-spores ; 

 and finally, that animal cells and the lowest unicellular organisms 

 very frequently possess no cell-membrane, but appear as naked 



