XIV BIOLOGICAL SCIENCES AND MEDICINE 349 



the economy, or they may favour it. On the other 

 hand, they may be of such a nature as to impede 

 the activities of the organism, or even to involve 

 its destruction. 



In the first case, these perturbations are ranged 

 under the wide and somewhat vague category of 

 " variations" ; in the second, they are called lesions, 

 states of- poisoning, or diseases ; and, as morbid 

 states, they lie within the province of pathology. 

 No sharp line of demarcation can be drawn between 

 the two classes of phenomena. No one can say 

 where anatomical variations end and tumours begin, 

 nor where modification of function, which may at 

 first promote health, passes into disease. All that 

 can be said is, that whatever change of structure 

 or function is hurtful belongs to pathology. Hence 

 it is obvious that pathology is a branch of biology ; 

 it is the morphology, the physiology, the distribu- 

 tion, the aetiology of abnormal life. 



However obvious this conclusion may be now, it 

 was nowise apparent in the infancy of medicine. 

 For it is a peculiarity of the physical sciences 

 that they are independent in proportion as they 

 are imperfect ; and it is only as they advance that 

 the bonds which really unite them all become 

 apparent. Astronomy had no manifest connection 

 with terrestrial physics before the publication of 

 the " Principia " ; that of chemistry with physics 

 is of still more modern revelation ; that of physics 

 and .chemistry with physiology, has been stoutly 



