46 MARRIAGE AND DISEASE. 



presenting extreme variation from the normal cannot 

 continue his like, and were it not for this law of reversion 

 the offspring of all such must succumb. 



Although this law is continually in action, guarding 

 jealously the family type against gross contamination, 

 its action is most commonly only observed in those 

 cases in which the variation from the normal is 

 marked. Should the variation be only slight this 

 principle of reversion is less active, the new character 

 is often transmitted in such cases, and in the course 

 of some generations may become a fixed and constant 

 character in the family. In this way new varieties 

 and races are built up. But should the variation be 

 extreme, whether recent and unstable, the result of 

 some inharmonious action of the various influences 

 at work, or the outcome of several generations of in- 

 judicious breeding, Nature revolts against the innova- 

 tion and throws back to the original. 



Of the working of this law of reversion we have 

 proof on every hand. If we take a person belonging 

 to some decidedly abnormal variety, as, say, the giant 

 (physiological), or the deeply phthisical (pathological), 

 we shall see how it acts. If either of these marry one 

 belonging to the same abnormal type as himself, there 

 will either be no offspring, or, if there be, it will show 

 a marked tendency to perpetuation of the abnormality 

 of the parents, and this deepening with each genera- 

 tion, the necessarily fatal type will soon be reached 

 and the family be at an end. Here with the junction 

 of Like abnormal persons, the law of reversion has little 



