2 INTRODUCTION. 



grows old are associated with a more or less striking decom- 

 position of its tissue elements. 



§ 4. Those alterations in the tissues which occur during 

 disease are of far greater moment to the physician. They are 

 })recisely similar to those which occur as a consequence of age. 

 Not w^ithout reason has Virchoiv compared the retrogressive pro- 

 cesses of disease w^ith a kind of premature old age. The ex- 

 istence of the individual cell, like that of the organism in its 

 entirety, must oscillate between birth and death. We must 

 therefore regard development and decay as the main categories 

 under which all moi-bid tissue changes naturally fall. But it 

 would be unfair to omit all mention of the fact that the histolo- 

 gical phenomena in the domain of pathology are far more various 

 than those attending the normal course of growth and decay. 



§ 5. Nearly every disease which is accompanied by ana- 

 tomical lesions exhibits a complex co-existence and succession of 

 progressive and retrograde processes. To these, taken together, 

 the naked-eye appearances of a diseased lung or liver are due. 

 Our task in the first part of this treatise will be to disentangle 

 the threads of this complicated web, and to examine each of the 

 progressive and retrograde processes singly and from ever}- point 

 of view, so that, in the second part, we may be able to construct 

 the morbid anatomy of particular diseases out of elements which 

 are already familiar. 



