66 INTRODUCTION. 



its data with the facts and laws of normal morphology and normal phys- 

 iology. While he should be conscious always on the one hand of the 

 invisible molecular changes which underlie the manifestations of energy, 

 and on the other will not ignore the details of gross morphology, his at- 

 tention will be most constantly drawn to the cells as the life units upon 

 which ultimately both the form and function of living things depend. 

 He will realize that as the cells of the normal body are what they are in 

 form and in function because of the conditions under which they have 

 been slowly evolved, and are at the moment placed ; so when the condi- 

 tions change and become abnormal, it is to the cells that he must look 

 for an understanding of the aberrations and disturbances by which we 

 recognize disease. 



In normal physiology attention is most keenly centred to-day upon 

 the structure and performances of cells as the field richest in the prom- 

 ise of significant revelations. So, also, in pathology by similar methods 

 and with equal persistence must the structure and performances of cells 

 under abnormal conditions be studied if we are to hope with reason for 

 a clearer comprehension of disease. This has long been recognized, and 

 to the conception of the pathological processes as essentially cellular 

 processes are due the great advances which this phase of biological science 

 has made during the past few decades. But the newer knowledge of the 

 cell, not as a membranous bag nor as a mere lump of protoplasm but as 

 a complex machine whose various structural features are of the utmost 

 significance, has greatly widened the field of cellular pathology. 



Manifestations of heredity which are displayed in the body as a 

 whole have long been known. To-day we may and must take account 

 of the marks of heredity in individual cell life. Not a few of what we 

 call the aberrances of cells in disease are but the expression of cell traits 

 and capacities latent in the environment which has become the usual and 

 therefore the normal, but finding expression as the sway of the body- 

 organism is released under disturbances of its equilibrium. Thus cells 

 thrown out of function may in a measure revert in character to less dif- 

 ferentiated types, and cells long comparatively quiescent may under 

 varying stimuli assume capacities and forms which they seemed to have 

 outgrown. 



Of course in the pursuit of pathological morphology it is the dead 

 body and dead tissues with which we are most often engaged. But these 

 are of special interest only as they reveal structures or indicate processes 

 which were maintained during life. So that he who can most closely 

 correlate the knowledge of the living cells with his observations upon 

 those which are dead will gain most from his morphological studies. 



While the pathology of to-day is essentially a cellular pathology, 

 while it is illuminating and convenient to consider the cells as physio- 

 logical and structural units, maintaining a certain independence of ex- 

 istence and function, it is nevertheless true that beyond their mere jux- 

 taposition in the body, beyond a close mutual dependence upon the 

 common blood supply and nerve control, there is a subtle and as yet 



