ANATOMY AND PHYSIOLOGY 



Schleiden also, what the word ordinarily implies a cav- 

 ity walled in on all sides. He conceived that the ulti- 

 mate constituents of all tissues were really such minute 

 cavities, the most important part of which was the cell 

 wall, with its associated nucleus. He knew, indeed, 

 that the cell might be filled with fluid contents, but he 

 regarded these as relatively subordinate in importance 

 to the wall itself. This, however, did not apply to the 

 nucleus, which was supposed to lie against the cell 

 wall and in the beginning to generate it. Subsequent- 

 ly the wall might grow so rapidly as to dissociate itself 

 from its contents, thus becoming a hollow bubble or 

 true cell; but the nucleus, as long as it lasted, was sup- 

 posed to continue in contact with the cell wall. Schlei- 

 den had even supposed the nucleus to be a constituent 

 part of the wall, sometimes lying enclosed between 

 two layers of its substance, and Schwann quoted this 

 view with seeming approval. Schwann believed, how- 

 ever, that in the mature cell the nucleus ceased to be 

 functional and disappeared. 



The main thesis as to the similarity of development 

 of vegetable and animal tissues and the cellular nature 

 of the ultimate constitution of both was supported by 

 a mass of carefully gathered evidence which a multi- 

 tude of microscopists at once confirmed, so Schwann's 

 work became a classic almost from the moment of its 

 publication. Of course various other workers at once 

 ited Schwann's claim to priority of discovery, in 

 particular the English microscopist Valentin, who as- 

 serted, not without some show of justice, that he was 

 working closely along the same lines. But so, for that 

 matter, were numerous others, as Henle, Turpin, Du- 



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