IDEAL TYPE OF A CELL. 5 



of animal tissues which, is more suggestive of comparison with 

 that which the botanists call a cell. (See p. 6.) 



All animal cells were at this time considered to be con- 

 structed on the same principle, being held to possess a cell wall, 

 enclosing a cavity, in which were fluid contents and a nucleus ; 

 when the membrane was not visible, it was either supposed 

 to have burst, or was admitted to be present. In the cells of 

 the egg a membrane was recognised by Krause,* from the 

 presence of a double contour line. This mode of proof was not, 

 however, strongly supported. C. H. Schultz considered he was 

 able to exhibit the membrane of the blood corpuscles by the 

 action of water upon them, inasmuch as they swelled up in 

 this fluid, and assumed a spherical form; he also believed 

 the nucleus revolved in the interior of the sphere. 



The corpuscles of pus and of mucus had, however, even in 

 the eyes of Schwann no distinctly demonstrable membrane; 

 he regarded them as minute roundish masses, containing a 

 nucleus, which might be termed cells, because this was the 

 elementary form of all animal and vegetable cells. 



In accordance with the general views of Schwann, respecting 

 the analogy of animal and vegetable cells, the ideal type of a 

 cell was constructed. 



Individual and scattered opposition to this ideal type of a 

 cell was ineffectual so long as the whole theory of Schwann 

 was contested, as it was, for example, by Arnold.f 



With sure footing, and still resting on Schwann's conclusions, 

 Leydig also abandoned the scheme of cell construction already 

 mentioned.^ He maintained that the contents of the cell are 

 of higher dignity than the membrane, and constitute the mate- 

 rial basis for the sensible and irritable processes ; and that the 

 conception of a cell requires the presence of only a little 

 mass of substance, inclosing a nucleus. The cell membrane 

 is, in his view, only the hardened external layer of the cell 

 substance. 



Max Schultze was, however, the first who effectually directed 



* Miiller's Archiv, 1837, p. 139. 



t See his Anatomie, 1845, Band i., p. 144. 



J Loc. cit. 



