110 CARNEGIE INSTITUTION OF WASHINGTON. 



A second discovery of importance has recently been made here by 

 Blakeslee and Belling, namely, that some of the irregular breeding 

 behavior of the jimson weed (Datura) is due to irregularity of chromo- 

 some-division in cell-division, resulting in extra chromosomes in some 

 gametes and a deficiency in others. This behavior is Uke that dis- 

 covered by Miss Lutz in the primroses at this Station 13 years ago, 

 which was the starting-point for the great development of our knowl- 

 edge of the relation between somatic mutations and chromosome va- 

 riation. The recent discovery establishes that there are two forms of 

 mutations : one due to extrachromosomal changes or, better, changes in 

 number of chromosomes, and one due to intrachromosomal changes, 

 to changes in the genes. 



A third capital discovery is that in a strain of mice susceptible to a 

 particular tumor the susceptibihty is not only found to be hereditary, 

 but it is shown that the hereditary factors are probably 4, though possi- 

 sibly 3 or 5 in number. This discovery makes much more definite the 

 previously known fact of inheritance of cancer in mice, and gives an 

 explanation of the failure to find a simple Mendelian explanation of in- 

 heritance of cancer in man. The inheritance is Mendelian, but there 

 are many factors and not merely a single factor involved. 



A fourth matter, whose study is now completed, was described in 

 a preliminary way in last year's report. It is the demonstration 

 that the effects of alcohoUzation of breeding rats show themselves in 

 the grandchildren of such rats. Not, indeed, in the gross fashion 

 described by Stockard in the case of his guinea-pigs, but by a certain 

 stupidity or inability to learn and take advantage of experience. No 

 other experiment of this sort approaches in careful control this series 

 of MacDowell. One may confidently assert, therefore, that the delete- 

 rious influence of alcoholism on even remote progeny lias been proved. 



Again, there has been demonstrated by Riddle a chemical difference 

 between male and female pigeon embryos, inasmuch as relatively more 

 female than male embryos withstand a diminished oxygen pressure, 

 indicating that they have a lower metaboHsm than male embryos. 

 Thus, the fundamental difference in metabolism of the two sexes has 

 been demonstrated for pigeons in their germinal, embryonic, and adult 

 stages. 



Finally, the theory of lethal, or loss of vital, factors has been extended 

 to human heredity by Dr. Little, who finds clear evidence of sex-linked 

 lethal factors in color-blind and hemophilic (bleeding) families, in con- 

 sequence of which there is a larger proportion of males that are color- 

 blind than would otherwise be expected. 



