SOME POSSIBLE BEARINGS OF GENETICS ON PATHOLOGY 1 1 



self-fertilized, the progeny in the next generation shows a still 

 wider range of variation, extending from that of the shorter 

 grandparent to that of the longer. Both grandparental cobs have 

 reappeared, but also many intermediate grades, Fig. 5. 



Such cases were formerly spoken of as blended inheritance. 

 It was supposed that the materials of the two parents have, as it 

 were, fused in the offspring and have remained fused. Today we 

 have a better explanation. It is this. Besides two major factors 

 that here determine cob length, there are other minor factors, 

 some of which make the short cob longer, others that make the 

 long cob shorter. These go over into the first generation hybrids, 

 and are sorted out in the germ cells of the hybrid. Consequently, 

 when the F/s are inbred, there are all sorts of recombinations of 

 the minor factors. This explains the greater variability of the 

 second generation. 



It is probable that in most of our domesticated animals, includ- 

 ing man, much of the variability is due to multiple factors, which 

 makes a study of inheritance in these groups extremely difficult, 

 especially when, as in the case of man, the number of offspring 

 from a pair is small, and critical combinations for study can not 

 be made. 



If then it is highly improbable that any particular defective 

 trait could ever become widely spread in the human germ-plasm, 

 how does it come about that such defects as feeblemindedness and 

 insanity are so widespread in the racial inheritance? There are 

 several possibilities here to keep in mind, but I think we ought not 

 to pretend that we can give a completely satisfactory account of 

 the situation. 



First. While the chance is heavily against any one defect es- 

 tablishing itself, there is always the possibility that some one de- 

 fect may establish itself. It must be remembered that while many 

 defective strains may be lost, one would notice only those that had 

 taken root. It is the presence of these that may give us an exag- 

 gerated idea of the generality of such occurrences. 



