1 50 THE BEGINNINGS OF LIFE. 



emphatically declared by Max Schultze \ that a distinct 

 investing membrane or cell-wall was not an essential 

 character : afterwards the typical cell was still further 

 shorn of its characteristics when it was shown (if 

 this had not been already done by Naegeli and Braun) 

 by Briicke 2 , Kiihne 3 , and others, that even the nucleus 

 was a non-essential constituent of that body, which 

 was formerly thought to represent not only the morpho- 

 logical, but also the vital unit. So that, in place of 

 the old c ceir with its definite characters, this would 

 reduce us to a mere naked, non-nucleated bit of pro- 

 toplasm as the simplest material substratum adequate 

 to display all those vital manifestations which were 

 previously considered as the essential attributes of cer- 

 tain formed elements known as 'cells.' The power 

 of displaying vital manifestations was, in fact, trans- 



1 ' Reichert und Du Bois Raymond's Archiv,' 1861. A mere mass of 

 protoplasm with a nucleus was sufficient to constitute a ' cell ; ' and at 

 the same time it was maintained that the substance of the cell (or that 

 within the wall, where this existed) was protoplasm, a contractile sub- 

 stance answering to what Dujardin had named sarcode. These later 

 modifications are, however, by no means antagonistic to the notions of 

 Schwann as may be gathered from the following passages : ' There is 

 no contradiction involved in the supposition that a nucleus may be 

 contained in a solid globule as well as in a cell. ... A given object may 

 really be a cell when even the common characteristics of that structure, 

 namely the perceptibility of the cell membrane, and the flowing out of 

 the cell contents, cannot be brought under observation. . . . The most 

 important and abundant proof as to the existence of a cell is the pre- 

 sence or absence of the nucleus.' Loc. cit. p. 37. 



2 'Wiener Sitzungsberichte,' 1861, pp. 18-22. 



3 'Protoplasma und die Contractilitiit.' Leipzig, 1864. 



