^^^ THE POPULAR SCIENCE MONTHLY. 



keepers of pet animals who take pride in the perfections of those they 

 have bred ; the florists, professional and amateur, who obtain new va- 

 rieties and take prizes ; form a body of men who furnish naturalists 

 with countless of the required proofs. But there is no such body of 

 men, led either by pecuniary interest or the interest of a hobby, to as- 

 certain by experiments whether the effects of use and disuse are inher- 

 itable. 



Thus, then, there are amply sufficient reasons why there is a great 

 deal of direct evidence in the one case and but little in the other— such 

 little being that which comes out incidentally. Let us look at what 

 there is of it. 



Considerable weight attaches to a fact which Brown-Sequard dis- 

 covered, quite by accident, in the course of his researches. He found 

 that certain artificially-produced lesions of the nervous system, so 

 small even as a section of the sciatic nerve, left, after healing, an in- 

 creasing excitability which ended in liability to epilepsy ; and there 

 afterward came out the unlooked-for result that the offspring of guinea- 

 pigs which had thus acquired an epileptic habit such that a pinch on 

 the neck would produce a fit, inherited an epileptic habit of like kind. 

 It has, indeed, been since alleged that guinea-pigs tend to epilepsy, 

 and that phenomena of the kind described occur where there have 

 been no antecedents like those in Brown-Sequard's case. But consid- 

 ering the improbability that the phenomena observed by him happened 

 to be nothing more than phenomena Avhich occasionally arise naturally, 

 we may, until there is good proof to the contrary, assign some value 

 to his results. 



Evidence not of this directly experimental kind, but nevertheless 

 of considerable weight, is furnished by other nervous disorders. There 

 is proof enough that insanity admits of being induced by circumstances 

 which, in one or other way, derange the nervous functions — excesses 

 of this or that kind ; and no one questions the accepted belief that 

 insanity is inheritable. Is it alleged that the insanity which is inherit- 

 able is that which spontaneously arises, and that the insanity which 

 follows some chronic perversion of functions is not inheritable ? This 

 does not seem a very reasonable allegation, and until some warrant 

 for it is forthcoming, we may fairly assume that there is here a fur- 

 ther support for belief in the transmission of functionally-produced 

 changes. 



Moreover, I find among physicians the belief that nervous disor- 

 ders of a less severe kind are inheritable. Men who have prostrated 

 their nervous systems by prolonged overwork or in some other way, 

 have children more or less prone to nervousness. It matters not what 

 may be the form of inheritance — whether it be of a brain in some way 

 imperfect, or of a deficient blood-supply ; it is in any case the inherit- 

 ance of functionally-modified structures. 



