

MODE OF ORIGIN OF CELLS. 35 



and that his well-grounded statement, made in 1855, " Omnis 

 cellula e cellula," really constitutes the basis of our present 

 cell theory. 



Whilst these fundamental propositions respecting the mode of 

 cell formation in compound bodies were advanced and main- 

 tained on the one side, Pasteur proved by brilliant experiments 

 that the statements made respecting the spontaneous origin of 

 various organisms in fluids were erroneous, and that when all 

 access of living organisms into such fluids was prevented, no 

 development could be proved in any case to occur. Every one 

 must admit that the general tendency of these facts is to dis- 

 prove that a free extracellular formation of cells ever takes 

 place. At the same time we are not justified in maintaining that 

 such a mode of formation never occurs ; it may, however, be said 

 that at the present time not one observation has been made, in- 

 contestably demonstrating the existence of a generatio sequivoca. 



We distinguish three forms of cell multiplication, one by 

 fission, one by gemmation, and, lastly, an endogenous mode. 

 According to Briicke, the last differs from the two former 

 in the circumstance that the cells originate like embryoes in 

 the interior of the parent cell, and gradually increase in size, 

 whilst in the other cases the substance of the mother cell 

 breaks up into fragments, which constitute the second gene- 

 ration. 



In the multiplication of nucleated cells by division the 

 nucleus, as a rule, first divides ; becoming elongated, then finger- 

 biscuit shaped, and finally constricted into two portions, which 

 recede from one another. The fission of the nucleus is not in all 

 instances followed by division of the cell, though it is usually 

 associated with the process of cell multiplication. Instances 

 are known where cells become greatly enlarged, whilst 

 their nuclei increase in number, either regularly or irregu- 

 larly, to twenty or more ; and in which, nevertheless, division 

 of the cell itself has not been observed to occur. Division of 

 the nucleus external to the cell, as has been already stated, has 

 not as yet been shown to take place. 



The formation of fresh nuclei within cells must be admitted 



Virchow's Archiv, 1855, Band viii., Heft 1. 



