THE PRESENT POSITION OF CELL-THEORY. 95 



whose views are not so exact, and who habitually commit 

 themselves to statements which on careful examination may 

 prove to be altogether untenable. 



It was pointed out some time since by Whitman, 1 and I 

 have since emphasised the fact, 2 that in his broad generalisa- 

 tions Schwann defined the cell-theory in a very exact manner, 

 and that the words originally used by him are perfectly 

 applicable to the cell-theory as it has been held up to the 

 present time. In saying this, I do not forget that Schwann 

 held some very erroneous views as to the nature and 

 structure of cells, which he regarded as vesicles, filled with 

 fluid, which made their appearance in a structureless matrix, 

 named for this reason, a cytoblastema. But Schwann's 

 work consisted of two parts, a statement of observations, 

 which have proved to be entirely erroneous, and a theory 

 of organisation, which has been very fruitful of results. He 

 was careful to say that his theory was only a provisional 

 explanation which suited the facts as nearly as possible, and 

 it is a great merit of the theory that it afforded such an in- 

 sight into organisation that the essential part of it did not 

 cease to be serviceable long after the "facts" on which it 

 was founded were shown to be, for the most part, false. 

 We need not therefore concern ourselves with the fact that 

 Schwann's conceptions of the origin and structure of cells 

 were false, but we may examine his theory and see how 

 much of it we may hold to, and how much we must reject 

 at the present day. 3 



Schwann was a very cautious writer, and the quotations 

 which are given below will dispose effectually of the state- 



1 C. O. Whitman, "On the Inadequacy of the Cell-theory of Develop- 

 ment, "Journal of Morphology, viii., p. 639, 1893. 



2 G. C. Bourne, "A Criticism of the Cell-theory," Quart. Jour. Micro- 

 scopical Science, xxxviii., p. 137, 1895. 



3 A large part of Schwann's theory of cells, viz., that part of it which 

 compared cell-formation to the process of crystallisation, was soon shown 

 to be untenable. But as this part was based on his erroneous views on 

 the structure and origin of cells, I have passed it over, since the falsity of 

 his views on this subject involved the falsity of as much of his theory as 

 was founded on them. 



