288 ON GROWTH AND OVERGROWTH 



if we can only determine it, then we can proceed to establish 

 the true theory of tumour formation. 



I need not say that there have been many attempts to form 

 such an adequate theory, from that of Cohnheim, who, ignorant 

 of the existence of the one group, sought to ascribe everything 

 to "cell rests," to those of present-day writers, who, heedless 

 of the existence of the other group, seek to ascribe everything 

 to microbes. Neither extreme, as I have shown, is possible. 

 I trust that I shall be forgiven if neglecting, on account of the 

 demands of time, to put before you what I may term intermediate 

 theories in full detail (of which those most discussed pro and 

 con at the present time are the theories of Ribbert 1 and Hanse- 

 mann.) 2 I here give rein to my own line of thought. 



Let me, in the first place, put before you in concise language 

 the problem that has to be solved : (1) Certain tumours arise 

 from misplaced cells ; (2) certain tumours arise from cells origin- 

 ally in normal position. What is the cause of either category 

 of cells taking on excessive growth independent of the needs of 

 the organism ? 



THE RELATION OP GROWTH TO FUNCTIONAL ACTIVITY OP CELLS 



To solve this problem it is clear that in the first place we 

 must have right ideas as to the nature of cell growth and pro- 

 liferation in ordinary. Now, as I pointed out a few months ago 

 (in the Jacobi Festschrift 3 ), we are apt to have a vague idea, to 

 say the least, of the nature of the normal growth of tissues. 

 The more one studies what occurs in the various tissues, the 

 more obvious it is that multiplication and the active performance 

 of other function by the cell are incompatible, or otherwise, that 

 the actively functioning and fully developed cell, as such, does 

 not undergo mitosis and show evidences of multiplication. 



In not a few tissues (the epidermis, periosteum, etc.) there 

 are present what may be termed proliferous or " mother cells " 

 cells which themselves throughout life do not attain full differ- 

 entiation, but which give oft daughter cells, and the daughter 

 cells it is which develop into the fully differentiated functional 



1 Ribbert, Das pathologische Wachstum der Gewebe, etc., Bonn (Cohen), 1896. 

 ' Hansemann, Die mikroscop. Diagnose der bosartigen Geschwulste,, Berlin 

 (Hirschwald), 1897. See p. 263. 



