XIII.] THE BIOLOGICAL SCIENCES AND MEDICINE. 327 



line of demarcation can be drawn between the two 

 classes of phenomena. No one can say where ana- 

 tomical 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 hurt- 

 ful belongs to pathology. Hence it is obvious that 

 pathology is a branch of biology; it is the morphology, 

 the physiology, the distribution, the aetiology of ab- 

 normal 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 revela- 

 tion ; that of physics and chemistry with physiology, 

 has been stoutly denied within the recollection of most 

 of us, and perhaps still may be. 



Or, to take a case which affords a closer parallel 

 with that of medicine. Agriculture has been culti- 

 vated from the earliest times, and, from a remote 

 antiquity, men have attained considerable practical 

 skill in the cultivation of the useful plants, and have 

 empirically established many scientific truths concern- 

 ing the conditions under which they flourish. But, it 

 is within the memory of many of us, that chemistry 

 on the one hand, and vegetable physiology on the 



