Sept. 26, 1889] 



NATURE 



529 



would not admit of it. But there are some aspects of the theory 

 which would need to be referred to in connection with the subject 

 now before us. It may be admitted that many variations which 

 may arise in the development of an individual, and which are of 

 service to that individual, would tend to be preserved and 

 perpetuated in its offspring by hereditary transmission. But it 

 is also without question that variations which are of no ser\'ice, 

 and, indeed, are detrimental, to the individual in which they 

 occur, are also capable of being hereditarily transmitted. This 

 statement is amply borne out in the study of those important 

 defects in bodily structure which pathologists group together 

 under the name of Congenital Malformations. I do not require 

 to go into much detail on this head, or to cite cases in which the 

 congenital defect can only be exposed by dissection, but may 

 refer, by way of illustration, to one or two examples in which 

 the defect is visible on the surface of the body. The commonest 

 form of malformation the hereditary transmission of which has 

 been proved is where an increase in the number of digits on the 

 hands or feet, or on both, occurs in certain families, numerous 

 instances of which have now been put on record. But in other 

 families there is an hereditary tendency to a diminution in the 

 number of digits or to a defect in the development of those 

 existing. I may give an illustration which occurred in the 

 family of one of my pupils, the deformity in which consisted in 

 a shortening or imperfect growth of the metacarpal bone of the 

 ring finger of the left hand, so that the length of that finger was 

 much below the normal. This family defect was traceable 

 throughout six generations, and perhaps even in a seventh, and 

 was, as a rule, transmitted alternately from the males to the females 

 of the family {Jo^crn. Anat. and Pliys., vol. xviii, p. 463) — 



F? 

 I 



M 



I 



F 



I 



M 



I 

 F 



I 



M 



M 



M 



M 



M 



In this and the following diagrams M stands for male, F for female, whilst 

 the block type (M or'F) marks the individual or generation in which the 

 •variation occurred. 



Another noticeable deformity which is known to be here- 

 •ditary in some families, and which may be familiar to some of 



my auditors, is that of imperfect development of the upper lip and 

 roof of the mouth, technically known as hare-lip and cleft palate. 



These examples illustrate what may be called the coarser kinds 

 of hereditary deformity, where the redundancies or defects in 

 parts of the body are so gross as at once to attract attention. 

 But modifications or variations in structure that can be transmit- 

 ted from parent to offspring are by no means limited to changes 

 which can be detected by the naked eye. They are sometimes 

 so minute as to be determined rather by the modifications which 

 they occasion in the function of the organ than by the ready recog- 

 nition of structural variations. One of the most interesting of these 

 is the affection known as Daltonism, or colour-blindness, which 

 has distinctly been shown to be hereditary, and which is due, ap- 

 parently in the majority of cases, to a defect in the development 

 of the retina, or of the nerve of sight which ends in it, though in 

 some instances they may be occasioned by defective development 

 of the brain itself. Dr. Horner has related a most interesting 

 family history (cited in " Die Allgemeine Pathologic," by Dr. 

 Edwin Klebs, Jena, 1887), in which the colour-blindness was traced 

 through seven generations. In this family the males were the 

 persons affected, though the peculiarity was transmitted through 

 the females, who themselves remained unaffected. The family 

 tree showed that in the sixth generation seven mothers had 

 children. Their sons, collectively nine in number, were all 

 colour-blind with the exception of one son, while none of their 

 nine daughters showed the hereditary defect. (See diagram 

 below.) 



The eye is not the only organ of sense which exhibits a ten- 

 dency to the production of hereditary congenital defects. The 

 ear is similarly affected, and intimately associated with congeni- 

 tal deafness is an inability to speak articulately, which occasions 

 the condition termed Deaf-mutism. Statisticians have given 

 some attention to this subject, both as regards its relative 

 frequency and its hereditary character. The writer of the article 

 "Vital Statistics," in the Report of the Irish Census Commis- 

 sioners during the decades ending 1851, 1861, 1871, has dis- 

 cussed at some length the subject of congenital deaf-mutism, and 

 has produced a mass of evidence which proves that it is often 

 hereditarily transmitted. In the Census Report for 1 87 1 (vol. Ixxii. 

 Part II., " Report on the Status of Disease," p. i, 1873), 3297 

 persons were returned as belonging to this class, and in 393 cases 

 the previous or collateral branches of the family were also mute. 

 In 211 of these the condition was transmitted through the 

 father ; in 182 through the mother. In 2579 cases there was 

 one deaf-mute in a family ; in 379 instances, two ; in 191 families, 

 three ; in 53, four ; in 21, five ; in 5, six ; and in each of two 

 families no fewer than seven deaf-mutes were born of the same 

 parents. In one of these two families neither hereditary predis- 

 position nor any other probable physiological or pathological 

 reason was assigned to account for the peculiarity, but in the 

 other family the parents were first cousins. Mr. David Buxton, 



M 



F 



I 



M 



F 

 I 



M 



M 



M 



M 



I 



M 



I " I 

 U M 



M 



M 



M 



M 



M M 



M 



I I I 



F F F 



who has paid great attention to this subject {Liverpool Medico- 

 Chirnrg. Journ., July 1857 ; January 1859), states that the 

 probability of congenital deafness in the offspring is nearly seven 

 times greater when both parents are deaf than when only one is 

 so ; in the latter case the chance of a child being born deaf is 

 less than three-quarters per cent. ; in the former, the chances are 

 that 5 per cent, of the children will be deaf-mutes. Mr. Buxton 



refers to several families where the deaf-mutism has been trans- 

 mitted through three successive generations, though in some 

 instances the aff'ection passes over one generation to reappear in 

 the next. He also relates a case of a family of sixteen persons, 

 eight of whom were born deaf and dumb, and one at least of the 

 members of which transmitted the affection to his descendants as 

 far as the third generation. There can be little doubt that con- 



