IDEAL TYPE OF A CELL. 7 



protoplasm lying in apposition with the inner surface of the cell wall. 

 The term protoplasm had already been brought into use by Remakfor 

 the contents of animal cells. Max Schultze proposed to apply the 

 term to the living mass of the cell, and since then the word proto- 

 plasm has been very generally employed. 



Max Schultze* takes the embryonal cell as the basis and 

 starting-point of his definition. " The most important cells," 

 he remarks, " those in which the fulness of cell life, the un- 

 limited power of tissue formation, is most distinctly evident, 

 are clearly the embryonal cells, which proceed from the division 

 of the cells of the ovum. We may see in these the true arche- 

 type of a cell, and yet they only consist of a little mass of 

 protoplasm and a nucleus. Both the nucleus and the proto- 

 plasm are products of the division of similar constituents of 

 another cell. Such cells include a living force in their interior, 

 essentially possessed by the protoplasm, although it is true 

 that the nucleus likewise plays an important part, not hitherto 

 known with sufficient accuracy. The protoplasm is no farther 

 isolated from external objects than by the circumstance that it 

 will not combine with the surrounding medium, and that it 

 constitutes, with the nucleus, a single whole. A distinct 

 membrane may, indeed, appear on the surface formed by the 

 conversion of the outer layer of the protoplasm, but then it 

 must be allowed to be an early indication of a retrograde 

 process. A cell invested by such a membrane can no longer 

 divide that is a power possessed by the enclosed protoplasm 

 alone. A cell with a membrane differentiated in its chemical 

 characters from the enclosed protoplasm, is like an encysted 

 infusorial animalcule." 



Bracket goes a step farther in his definition of a cell, 

 maintaining that no proof has been given that the nucleus 

 is indispensable to our conception of it. He rests his state- 

 ment essentially on the fact that cells are known to occur 

 in the cryptogamia in which no nucleus is visible. " We 

 have," he says, " no positive information, either respecting the 

 origin or the function of the nucleus ; even the constancy of 



* Loc. cit., p. 8. 



t Die Elementar-organismen, pp. 18 22'. 



