124 THE CAUSATION OF DISEASE. 



quagga, being short, stiff, and upright." * Many such cases 

 might be cited, but there is no need, for the principle in 

 question is so well recognized that no breeder would allow a 

 good animal to be crossed by one of inferior breed, for fear of 

 damaging the future progeny. 



Now, these considerations raise a question of some interest to 

 the physician. If the male, by impregnating the female, tends 

 to make all the future progeny like himself, one would expect 

 the second child of the same parents to be more like the father 

 than the first, for it would inherit the ordinary mean likeness 

 plus, an additional degree of likeness derived from the previous 

 impregnation, and this latter we may suppose to increase with 

 each successive impregnation by the same male ; so that, if such 

 is the case, each successive child should be more like the father, 

 and in consequence show a greater tendency to inherit disease 

 from him. Whether this inference is true or not, I cannot 

 say, but the subject is one deserving of investigation, and ] 

 should be somewhat surprised were it not found that the first 

 child is, on the whole, least like the father ; but I should not 

 be surprised if it were discovered that, after the second, each 

 successive child was not more like the father, because we can 

 well imagine that the sire, having once, by an impregnation, 

 influenced the mother in a particular way, may be incapable of 

 adding to this influence by subsequent impregnations. There 

 is no reason why the question should not be settled by a series 

 of experiments on animals and plants. 



Inheritance of Acquired Structural Characters. — Of 

 course characters once acquired tend to be inherited. Some 

 authors — even great ones — have been at much trouble to prove 

 that acquired characters, as well as inherited ones, may be 

 handed down by parents to their offspring. To me the fact 

 seems self-evident ; it matters little how a parent has come by 

 a character, for, according to the great doctrine of heredity, the 

 offspring tend to reproduce more or less exactly the likeness of 

 the parents. What we have seen is, that acquired characters 

 are less likely to be inherited than others, for they are not so 

 deeply impressed upon the organism. 



* " Animals and Plants under Domestication," vol. i. p. 436. 



