166 NATURAL INHERITANCE. [CHAP. 



ceding chapters. There are a certain number of recog- 

 nized groups of disease, which we may call A, B, C, &c., 

 and the proportion of persons who die of these diseases 

 in each of the two generations is the same. The pre- 

 liminary question to be determined is whether and to 

 what extent those who die of A in the second genera- 

 tion, are more or less often descended from those who 

 died of A in the first generation, than would have been 

 the case if disease were neither hereditarily transmitted 

 nor clung to the same families for any other reason. 

 Similarly as regards B, C, D, and the rest. 



This inquiry would be more difficult than those 

 hitherto attempted, because longevity and fertility are 

 both affected by the state of health, and the circum- 

 stances of home life and occupation have a great effect 

 in causing and in checking disease. Also because the 

 father and mother are found in some notable cases to 

 contribute disease in very different degrees to their 

 male and female descendants. 



I had hoped even to the last moment, that my 

 collection of Family Records would have contributed 

 in some small degree towards answering this question, 

 but after many attempts I find them too fragmentary 

 for the purpose. It was a necessary condition of success 

 to have the completed life-histories of many Fraternities 

 who were born some seventy or more years ago, that 

 is, during the earlier part of this century, as well as 

 those of their parents and all their uncles and aunts. 

 My Records contain excellent material of a later date, 

 that will be valuable in future years ; but they must 



