128 VEGETABLE CELLS. 



tion from the contents ; 2, Those in which the phenomena 

 do not oppose this hypothesis, and at the same time do 

 not afford the slightest probability to any other assump- 

 tion. Thus no objection can be made against the con- 

 clusion from analogy, so much the less that the examples 

 of the second category do not include any single point 

 not found in the first category which might suggest a 

 process of a different nature. 



From the foregoing discussions I must express the 

 definition of the formation of membrane in the following 

 terms : The cell-membrane is an investment lying upon 

 the surface of the contents > secreted by the contents them- 

 selves. The membrane of a cell is the product of its own 

 contents, as well in the beginning as subsequently. It 

 does not originate through the chemical action of one 

 substance upon another of different kind ; its formation 

 is an organic process, and in fact a process of secretion. 

 This theory of the formation of membrane is, as we have 

 seen, an immediate consequence of the facts, and avoids 

 those formal and material errors which are connected with 

 the theories of Schwann and Schleiden, and of which I 

 have spoken elsewhere in the definition of a cell. 



The other essential epoch in cell-formation is the in- 

 dividuali^ation of a portion of the contents, which becomes 

 transformed into a new cell. Here again we must, at the 

 outset, distinguish between normal and abnormal cell- 

 formation. In abnormal cell-formation, the mode in 

 which the contents become individualized does not de- 

 pend on a definite law, but on mere external, accidental 

 circumstances. Large or small, many or few, portions 

 of contents become isolated and form new cells. The 

 idea of individualization of portions of the contents is 

 here altogether vague, since it gradually loses itself in the 

 opposite process. 



I have already repeatedly noticed a series of phenomena 

 which the abnormal cell-formation presents in living cells. 

 The one extreme is exhibited where a minute free portion 

 of contents, composed of mucilage alone, becomes clothed 



