Diseases 127 



tions are of common occurrence. An organism is a 

 unity, even when it is an implicit organism, the germ- 

 cell ; the new must be congruent with the old. 



THE OPTIMISM OF PATHOLOGY 



In connection with new departures or variations 

 we venture to follow for a short distance a line of 

 thought that seems to give promise of illuminating 

 views. One of the foundations of modern pathology 

 was laid by Virchow about the time of the publication 

 of The Origin of Species. He showed that many of 

 the changes which are called diseases are exaggera- 

 tions or inhibitions of normal processes. That is to 

 say, constitutional diseases are not mysterious malig- 

 nant intrusions, but disturbances of an everyday 

 routine. A disease may be due to the invasion of the 

 body by some virulent microbe or microscopic beast 

 of prey or strength-sapping parasite. Or it may be 

 due to some serious defect in the nutrition or to some 

 radical unwholesomeness in habits and surroundings. 

 But when we put aside these parasitic diseases and 

 modificational diseases, there remain those that may 

 be called constitutional, which are due to some initial 

 perturbation in the germinal material — to some new 

 departure which is on the wrong side of viability. 

 What Virchow pointed out was that these new de- 

 partures which spell disease need not be very far 

 removed from those that are useful. A change that 

 misses the target in one kind of living creature may 

 be a bull's eye in another. Constitutional disease is 

 metabolism that has got out of time, out of place, and 



