452 EVOLUTION, GENETICS, AND EUGENICS 



excesses in eating or drinking may give a stimulus to its expression. 

 "The conclusion that I have arrived at," says Prof. D. J. Hamilton, 

 "is that the gouty habit of body has arisen as a variation, and as such 

 is hereditarily transmissible, and that excess of diet and alcohol merely 

 renders the habit of body apparent." It may also be pointed out that 

 gout and rheumatism and the like are rather processes of metabolism 

 than structural modifications, though the latter may ensue. 



After pointing out the irrelevancy of citing cases of the hereditary 

 recurrence of polydactylism, haemophilia, colour-blindness in man, 

 or the absence of horns in cattle or of tails in cats, as instances of the 

 transmission of acquired characters, Prof. Ernst Ziegler says: "Only 

 that can be regarded as ' acquired ' which is produced in the course of 

 the individual life, during and after the period of development, exclu- 

 sively under the influence of external conditions; the term is in no 

 wise applicable to peculiarities which, as one says, arise of themselves 

 from a predisposition already present in the germ." 



Misunderstanding IV. — Mistaking the reappearance of a modifica- 

 tion for transmission of a modification. — It is of little service to cite 

 cases where a particular modification reappears generation after gen- 

 eration unless it be shown that the change recurs as part of the inheri- 

 tance, and not simply because the external conditions which evoked it 

 in the first generation still persisted to evoke it in those that followed. 

 Reappearance is not synonymous with inheritance. 



Misunderstanding V. — Mistaking re-infection for transmission. — 

 A particular form of the fourth misunderstanding has to do with facts 

 so special that it may be conveniently treated of separately. It has 

 to do with microbic diseases. It is admitted that a parent infected 

 with tubercle-bacillus or with the microbe of syphilis may have off- 

 spring also infected. But such cases are irrelevant in the discussion. 

 Infection, whether before or after birth, has nothing to do with inheri- 

 tance. As Dr. Ogilvie says, "Wherever the transmission of infectious 

 disease from parent to offspring has been adduced to support the 

 doctrine of the inheritance of acquired characters, it has been done in 

 utter misconception of its meaning and scope." 



Medical men have sometimes condescended to make a subtle 

 distinction between "hereditary" and "congenital" syphihs — the 

 latter manifested at birth, the former some time afterwards! It seems 

 strange that they have failed to recognise that there is no reason to use 

 the word "hereditary" at all in this connection. What occurs is an 

 infection, and it is theoretically immaterial at what stage the infection 

 occurs. A microbe cannot be part of an inheritance. 



