OF LIVING MATTER 27 



central body known as the 'nucleus' together with a distinct cell 

 wall ; and Schleiden and Schwann in 1839, ^s a result of their 

 remarkable investigations, endeavoured to prove that all the tissues 

 of both plants and animals were entirely built up of such morpho- 

 logical units, named ' cells.' 



Some twenty years later Virchow announced ' views which had 

 an immense influence on pathological doctrines throughout all the 

 schools of medicine, and wherever biological studies were culti- 

 vated. He maintained that " the cell is really the ultimate morpho- 

 logical unit in which there is any manifestation of life, and that we 

 must not transfer the seat of real action to any point beyond the 

 cell." He denied altogether the origin of cells de novo in blaste- 

 mata after the fashion described by Schleiden. He held that cells 

 can be produced only from or by pre-existing cells. He did not 

 attempt to prove, however, that the whole bulk of the tissues is 

 made up exclusively of cells ; he admitted the existence of a large 

 amount of intercellular material in many tissues, and so, in order 

 to reconcile this fact with his previous doctrine, he was compelled 

 to put forward the hypothesis that such intercellular material may 

 be broken up into imaginary ' cell territories,' each of which is 

 influenced or ruled over by the cell lying in its midst. 



But important modifications as to the true conception of the 

 nature of a cell had been growing up even before the publication 

 of Virchow's theories. So far the cell has been spoken of as an 

 altogether definite structure : as a body with a distinct wall 

 or bounding membrane and certain contents, including among 

 other things one of [the most fundamental parts of the cell, 

 the ' nucleus.' But it was maintained by Nageli,^ and also by 

 Alexander Braun 3 and then more emphatically by Max Schultze, 

 that a distinct investing membrane or cell- wall was not an essential 

 character.t Afterwards the typical ultimate unit of life was still 

 further shorn of its characteristics when it was shown (if this had 

 not been already done by Nageli and Braun) by Briicke,s Kiihne,^ 



' ' Cellular Pathologic,' 1858. 



' ' Zeitschrift fur Wissen. Botanik,' 1846 (Transln. Ray Soc. 1849, p. 95). 



3 'The Phenomena of Rejuvenescence in Nature,' 1851 (Transln. Ray Soc. 1853). 



* ' Reichert and Du Bois Reymond'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 substance answering to what Dujardin had 

 named sarcode. 



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



' ' Protoplasma und die Contractilitat.' Leipzig, 1864. 



