XXVII HUMAN PROGRESS : PAST AND FUTURE 499 



closely resembled the corresponding cells and structures 

 in the parents at that particular epoch of their lives. Thus 

 was explained the transmission of disease, and the supposed 

 transmission of the changes produced in the parents by 

 use or disuse of organs or by other external conditions. 



To illustrate this by an example : if two brothers, 

 equally strong and healthy, became one a city clerk, the 

 other a farmer, land-surveyor, or rural postman, living 

 much in the open air and walking many miles every day 

 of his life, and if they married two sisters equally alike 

 in constitution, then the children of these two couples, 

 especially those born when their parents approached 

 middle age and the different conditions of their existence 

 had had time to produce its full effect on their bodily 

 structure, ought to show a decided difference, the one 

 family being undergrown, pale, and rather weak in the 

 lower limbs, the other the reverse; and this difference 

 should be observable even if the children of the two 

 families were brought up together under identical con- 

 ditions. It may be here stated that no trustworthy 

 observations have ever been made showing that such 

 effects are really produced, but it has always been be- 

 lieved that they must be produced. 



As Darwin's theory of Pangenesis led to considerable 

 discussion, Mr. Francis Galton, who had at first accepted 

 it provisionally, endeavoured to put it to the test of experi- 

 ment. He obtained a number of specimens of two 

 distinct varieties of domestic rabbits which breed true, 

 and, by an ingenious and painless arrangement, caused 

 a large quantity of the blood of one variety to be trans- 

 fused into the blood-vessels of the other variety. This 

 having been effected with a number of individuals 

 without in any way injuring their health, they were 

 separated and bred from. It was found that in every 

 case the offspring resembled their parents and showed 

 no trace of intermixture of the two varieties. It was 

 also pointed out by another critic that if the theory of 

 Pangenesis were true, the stock on which a fruit is 

 grafted ought to change the character of the fruit pro- 

 duced by the graft, which, as a rule, it does not do. 



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