NEO-LAMARCKIANISM. 263 



in food or physical conditions. But the chief agencies 

 in producing variations are habits of use and disuse 

 of various parts. Darwin, indeed, recognized this 

 factor, but believed it of slight importance. Neo- 

 Lamarckianism regards it as by far the most impor- 

 tant factor. 



That the use of an organ has great influence upon 

 its development in the individual so using it, is a 

 fact too well attested to admit question. The size 

 of the blacksmith's arm, the general development of 

 the body of the gymnast, the delicacy of the blind- 

 man's feeling, the acuteness of the musician's ear, 

 the degeneration of any organ whose use has dis- 

 appeared as a paralyzed arm, are all conclusive 

 proofs of this fact. Now, if continual use of an 

 organ results in an increase of its efficiency, and if, 

 further, the offspring of the animal so using it in- 

 herits this increased efficiency, it is evident that it 

 is no longer so difficult to understand the develop- 

 ment of organs. Physiology teaches us why it is 

 that increased use has this effect. Any use of a 

 part above the normal, causes an extra amount of 

 blood to flow to that part, and an increased activity 

 of its various cells. If, therefore, any organ become 

 of new value to its possessor, by reason of any 

 change in conditions, it will be used more, and 

 so long as it is thus used, its activities will increase, 

 and, consequently, its size and efficiency. If, now, 

 the offspring of such an individual has a tendency 

 to inherit the peculiarities of its parents, the second 

 generation will have the organ in question better 

 developed to start with than did its parents. During 



