BBITISH ASSOCIATION. 351 



I alluded in my first Address, a phenomenon which we suspect to be 

 at the bottom of various anomalies of heredity, and suggests that 

 there may be truth in the popular notion that in some respects sons 

 resemble their mothers and daughters their fathers. 



As to the descent of hereditary diseases and malformations, 

 however, we have abundant data for deciding that many are trans- 

 mitted as dominants and a few as recessives. The most remarkable 

 collection of these data is to be found in family histories of diseases 

 of the eye. Neurology and dermatology have also contributed many 

 very instructive pedigrees. In great measure the opthalmological 

 material was collected by Edward Nettleship, for whose death we so 

 lately grieved. After retiring from practice as an oculist he devoted 

 several years to this most laborious task. He was not content with 

 hearsay evidence, but travelled incessantly, personally examining all 

 accessible members of the families concerned, working in such a way 

 that his pedigrees are models of orderly observation and recording. 

 His zeal stimulated many younger men to take part in the work, and 

 it will now go on, with the result that the systems of descent of all 

 the common hereditary diseases of the eye will soon be known with 

 approximate accuracy. 



Give a little imagination to considering the chief deduction from 

 this work. Technical details apart, and granting that we cannot 

 wholly interpret the numerical results, sometimes noticeably more 

 and sometimes fewer descendants of these patients being affected 

 than Mendelian formulae would indicate, the expectation is that in 

 the case of many diseases of the eye a large proportion of the children, 

 grandchildren, and remoter descendants of the patients will be 

 affected with the disease. Sometimes it is only defective sight that 

 is transmitted ; in other cases it is blindness, either from birth or 

 coming on at some later age. The most striking example perhaps is 

 that of a form of night-blindness still prevalent in a district near 

 Montpellier, which has affected at least one hundred and thirty 

 persons, all descending from a single affected individual * who came 

 into the country in the seventeeth century. The transmission is in 

 every case through an affected parent, and no normal has been known 

 to pass on the condition. Such an example well serves to illustrate the 

 fixity of the rules of descent. Similar instances might be recited relating 

 to a great variety of other conditions, some trivial, others grave. 



At various times it has been declared that men are born equal, and 

 that the inequality is brought about by unequal opportunities. 

 x\cquaintance with the pedigrees of disease soon shows the fatuity of 

 such fancies. The same conclusion, we may be sure, would result 

 from the true representation of the descent of any human faculty. 

 Never since Galton's publications can the matter have been in any 

 doubt. At the time he began to study family histories even the broad 



* The first human descent proved to follow Mendelian rules was that of 

 a serious malformation of the hand studied by Farabee in America. Drink- 

 water subsequently worked out pedigrees for the same malformation in 

 England. After many attempts, he now tells me that he has succeeded in 

 proving that the American family and one of his own had an abnormal 

 ancestor in common, five generations ago. 



