218 TRANSMISSION OF ACQUIRED CHARACTERS 



Manly Miles gives two cases to illustrate what seems to him a 

 general fact, the occurrence of modification-inheritance in breeding : 

 " The fashion of raising lambs by nurses of other breeds, and drying 

 up the dam at once to keep her in show condition, resulted in seriously 

 diminishing the inherited capacity for milk production in the females 

 of the family as treated." " Cows on short pastures and under 

 careless management will form the habit of ' going dry ' early in 

 the season, and this habit of giving milk for a short period is not only 

 transmitted, but becomes a marked peculiarity of the females of the 

 family that is persisted in under better conditions of food supply." 



But these and numerous similar cases only show, what is univer- 

 sally admitted, that a nutritive disturbance in the mother is apt to 

 affect the nutritive vigour of the offspring. 



Brewer (cited by Cope, 1896, p. 436) reports what may be called 

 a good case. Sheep taken from a favourable region to one with 

 alkaline or salt soil, dry climate, and corresponding forage plants, 

 acquire a certain harshness in the wool. The change begins immedi- 

 ately, " but is more marked in the succeeding fleeces than in the 

 first. It is also alleged that the harshness increases with succeeding 

 generations, and that the flocks which have inhabited such regions for 

 several generations produce naturally a harsher wool than did their 

 ancestors, or do the new-comers." Of course, the second generation 

 would naturally have harsher wool than the new-comers, but if 

 harshness really increases with succeeding generations, the case is 

 one of the best as yet brought forward. 



Immunity. — Another typical line of evidence is based on the 

 study of immunity. To this very important, but very difficult, 

 subject we have referred in another chapter, but the particular 

 point here may be briefly stated. It is well known that some 

 natives are relatively immune to yellow fever ; this is now a 

 heritable quality ; the question is whether it can be regarded as 

 originally an acquired character. Was it in origin a modification 

 of the bodily metabolism subsequent upon the disease ? It 

 seems very difficult to adopt this interpretation, and most 

 authorities incline to the other alternative of regarding immunity 

 as a constitutional variation which has become dominant in the 

 race by the elimination of those members who were not immune. 



