1 66 HEREDITY 



referred to limbs or portions of limbs which have been 

 entirely removed by the hand of the surgeon. The 

 nerve centres, therefore, which correspond to the 

 severed parts still vibrate in the old manner, and if 

 this is so in regard to pain, it may be assumed that a 

 somewhat similar state of things would obtain in 

 respect to the transmission of hereditary impulses. 



Positive as well as negative influences deserve some 

 consideration. The former may be either good or 

 bad : they may exceed the normal degree of intensity, 

 or they may fall below it. It may possibly be that 

 when the influences proceeding from both parents are 

 opposed they act as mutual correctives, but, so far as 

 we know, there is no evidence on this point. It may 

 be also that a perfectly normal influence on the part 

 of one parent is sufficient to counterbalance abnormal 

 influences on the part of the other; this, however, 

 would seem to be more probable were the latter 

 deficient in intensity. But there are many abnor- 

 malities in the mode of functioning of the nervous 

 system which become, as it were, grafted on to it, and 

 are very frequently reproduced by hereditary trans- 

 mission. Let us suppose, for instance, that a couple 

 happens to be living in a very relaxing locality, and 

 that as a consequence the walls of their arteries 

 become somewhat flaccid, the circulation slow, and the 

 nerve-power generally diminished. Children born 

 from them under such conditions would probably 

 show some signs of languor and lack of vitality. On 

 the other hand, let us suppose that, as a result of long 



