PROGRESS IN ANATOMY AND PHYSIOLOGY 



Schwann propounded what soon became famous as his 

 cell theory, under title of Mikroskopische Untersuchun- 

 gen uber die Uebereinstimmung in der Structur und 

 dem Wachsthum der Thiere und Pflanzen. So expeditious 

 had been his work, that this book was published early 

 in 1839, only a few months after the appearance of 

 Schleiden's paper. 



As the title suggests, the main idea that actuated 

 Schwann was to unify vegetable and animal tissues. 

 Accepting cell-structure as the basis of all vegetable 

 tissues, he sought to show that the same is true of ani- 

 mal tissues, all the seeming diversities of fibre being but 

 the alteration and development of what were originally 

 simple cells. And by cell Schwann meant, as did Schlei- 

 den also, what the word ordinarily implies a cavity 

 walled in on all sides. He conceived that the ultimate 

 constituents of all tissues were really such minute cavi- 

 ties, 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. Subsequently 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 supposed to continue in 

 contact with the cell wall. Schleiden had even supposed 

 the nucleus to be a constituent part of the wall, some- 

 times lying enclosed between two layers of its substance, 

 and Schwann quoted this view with seeming approval. 

 Schwann believed, however, that in the mature cell the 

 nucleus ceased to be functional, and disappeared. 



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