752 COMPARATIVE PHYSIOLOGY. 



animals, but occurring in disease in others ; many will occur 

 on reflection. In considering many of these cases, we 

 must recognise the law of correlation, and realise that the 

 structures of a particular animal are not commonly the best 

 conceivable, but the best that can be attained under the 

 given conditions. 



Pathological new formations may arise in response to 

 mechanical stimulation, as in the case of corns and warts, 

 or may be due to aberrant physiological processes. Thus, 

 cancer is regarded by many as in origin an aberrant gland- 

 formation, and only occurs in regions of the body where 

 glands are normally found. It • is a senile modification of 

 an ordinary developmental process. Pathological bony 

 growths seem to have their origin in patches of cartilage 

 remaining from the primitive cartilage of limb or brain case, 

 and so are continuations of the ordinary process by which 

 cartilage is replaced by bone. 



Rudimentary or imperfectly formed organs are in general 

 specially liable to disease. Such rudimentary organs are 

 usually relics of past history. We must thus recognise that, 

 just as in the history of civilisation some of the most cruel 

 wrongs are only good institutions belated, so in the history of 

 disease the most dire pathological conditions may be histori- 

 cally only the result of belated physiological processes. In 

 some cases we may perhaps say more hopefully that patho- 

 logical processes may be the starting point for new physio- 

 logical evolutions. 



Brief as the above comparative survey of Physiology and 

 Pathology is, it may serve to give the student some impression 

 of the intricacy of life, and act as a relief from mechanical 

 theories of Variation, Selection, and Heredity. It is an 

 attempt to look from the inner side upon the great problem 



which is constantly being worked out before us : o-iven 



the potentialities of protoplasm and certain chemical and 

 physical conditions, to find the best adaptation to a o-iven 

 environment. 



