THE CAUSATION OF DISEASE. I I 3 



granulation-tissue, is one of dissolution, and how far it is 

 one of evolution. The exact origin of the cells composing 

 granulation-tissue is still a subject of dispute ; for, while all 

 pathologists agree that the majority of them are derived from 

 the blood, there is not yet complete agreement as to whether the 

 fixed cells of the affected part help in their formation. Now, if 

 allthe cells are derived from the blood, we must look upon the 

 process whereby a mature tissue is converted into granulation- 

 tissue as a complete dissolution, followed by a separate and 

 independent evolution ; but, if some of the cells, as is probably . 

 the case, are derived from the fixed cells of the part under- 

 going dissolution, it follows that the cells of the affected part 

 are, at one and the same time, undergoing dissolution and 

 evolution ; for, while the mature cells are breaking up and thus 

 descending from their high state of evolution, they are, at the 

 same time, giving birth to offspring, and this must be consi- 

 dered as a step in the direction of evolution. 



In such a disease as epithelioma, again, it is very difficult to 

 separate the two processes — dissolution and evolution. Let us 

 take the squamous variety. There is a great multiplication of 

 epithelial cells, and, in so far as this multiplication is at the 

 expense of mature cells, there is dissolution. The young 

 progeny, however, grow, or seem to grow, into mature cells. 

 There is, therefore, a more or less complicated evolution. But 

 the evolution is not complete ; we have seen that the word 

 11 structure " does not apply merely to the conformation of 

 individual cells, but also to the arrangement of them into 

 tissues, and in squamous epithelioma the arrangement of the 

 cells is imperfect ; wherefore, taking the tissue as a whole, it 

 is obvious that evolution is partial. 



But it matters little whether we can or cannot, in any given 

 instance of disease, mentally separate the two processes of 

 dissolution and evolution. The important fact for us, at this 

 place, is — that the local evolution in disease, alike with the 

 local dissolution, leads to reversion, or, more accurately, to a 

 series of reversions ; for while a cell or tissue is evolving, it 

 must, unless it evolve on lines entirely different from those on 

 which the species itself evolved — a thing obviously impossible 

 — pass through various phases cf past ancestral life. 



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