XIV BIOLOGICAL SCIENCES AND MEDICINE 349 



of 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 le- 

 sions, states of poisoning, or diseases; and, as mor- 

 bid states, they lie within the province of pathol- 

 ogy. No sharp line of demarcation can be drawn 

 between the two classes of phenomena. No one 

 can say where anatomical variations end and tu- 

 mours begin, nor where modification of function, 

 which may at first promote health, passes into dis- 

 ease. All that can be said is, that whatever change 

 of structure or function is hurtful belongs to pa- 

 thology. Hence it is obvious that pathology is a 

 branch of biology; it is the morphology,- the physi- 

 ology, the distribution, 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 appar- 

 ent. Astronomy had no manifest connection with 

 terrestrial physics before the publication of the 

 ''' Principia "; that of chemistr}'- with physics is 

 of still more modern revelation; that of physics 



