CHAPTEK I 



ON GROWTH AND OVERGROWTH AND ON THE RELATIONSHIP 

 BETWEEN CELL DIFFERENTIATION AND PROLIFERATIVE 

 CAPACITY ; ITS BEARING UPON THE REGENERATION OF 

 TISSUES AND THE DEVELOPMENT OF TUMOURS 1 



(1900) 



THERE are in medicine and other sciences not a few beliefs and 

 ideas which we have taken up we know not how, and which in 

 general we no more think of discussing than we do, for example, 

 the subject of good manners. Thus, just as it is difficult, if not 

 impossible, for us to state how or where we gained any single 

 article of our code of personal ethics, so it is with certain of 

 these general ideas in medicine ; and while we have never 

 discussed these beliefs, we feel individually assured that they are 

 the current ideas of other workers along the same lines. 



One of these tacit beliefs or comprehensions relates to the 

 subject of the growth of tissues. Asked off-hand we should 

 assuredly, each one of us, state as his familiar belief that muscle 

 arises from muscle, epithelium from epithelium, nerve cell from 

 nerve cell, and so on, and the mental picture which we form of 

 the process of growth is, I fancy (though here, of course, I speak 

 under correction), that the fully formed epithelial cell undergoes 

 mitosis and divides into two, and so with the cells of other tissues. 

 Yet if we think a little longer and recall what we have actually 

 seen under the microscope, this mental picture is seen to be 

 incorrect or, at least, imperfect. Thinking recently over this 

 matter it has been impressed upon me that if we obtain a correct 

 idea of what occurs during the process of growth of tissues, we 

 not only realize that there is a very broad biological law under- 



1 Published in the Festschrift in honour of Dr. Abraham Jacobi, New York, 

 1900, 422, and Medical Chronicle, Manchester, June 1900. 



