NECESSARY TRUTHS— EFFECTS OF EXPERIENCE. 087 



ing to Weismann, by good or bad nutrition. Through this 

 they may degenerate in various ways or lose vitality alto- 

 gether. They may also be infected through the blood by 

 small-pox, syphilis, or other virulent diseases, and other- 

 wise be poisoned. But peculiarities of neural structure and 

 habit in the parents tvhich the parents themselves luere not 

 horn ivith, they can never acquire unless perhaps accident- 

 ally through some coincidental variation of their own. 

 Accidental variations develojD of course into idiosyncrasies 

 which tend to pass to later generations in virtue of the 

 well-known law which no one doubts. 



Referring to the often-heard assertion that the increase 

 of talent found in certain families from one generation to 

 another is due to the transmitted effects of exercise of the 

 faculty concerned (the Bachs, the Bernoullis, Mozart, etc.), 

 he sensibly remarks, that the talent being kept in exercise, 

 it ought to have gone on growing for an indefinite number 

 of generations. As a matter of fact, it quickly reaches a 

 maximum, and then we hear no more of it, which is what 

 happens always when an idiosyncrasy is exposed to the ef- 

 fects of miscellaneous intermarriage. 



The hereditary ejjilepsy and other degenerations of the 

 operated guinea-pigs are explained by Professor Weis- 

 mann as results of infection of the young by the parent's 

 blood. The latter he supposes to undergo a pathologic 

 change in consequence of the original traumatic injury. The 

 obsolescence of disused organs he explains very satisfactor- 

 ily, without invoking any transmission of the direct effects of 

 disuse, by his theorj^ of panmixy, for which I must refer to 

 his own writings. Finally, he criticises searchingly the 

 stories we occasionally hear of inherited mutilations in 

 animals (dogs' ears and tails, etc.), and cites a prolonged 

 series of experiments of his own on mice, which he bred for 

 many generations, cutting off both parental tails each time, 

 without interfering in the least with the length of tail with 

 which the young continued to be born. 



The strongest argument, after all, in favor of the La- 

 marckian theory remains the a priori one urged by Spencer 

 in his little work (much the solidest thing, by the way, which 

 he has ever written) ' The Factors of Organic Evolution.' 



