10 



Scientific Proceedings (ioi). 



one fifth of the total calories) but with whole wheat instead of 

 white read or patent flour, young were successfully suckled 

 (though at the cost of considerable loss of weight on the part of the 

 mother) and are growing at somewhat less than the average rate. 



When about two fifths of the total calories were supplied by 

 milk and the rest by whole wheat, the mother has suckled the 

 young without undue loss of weight and the young have made a 

 fully normal rate of growth. 



When the market milk used has been replaced by dried milk, 

 or when it has been incorporated into the bread in bread-making 

 and, therefore, subjected to the heating involved in the baking 

 of the bread, there has been no evidence of any serious destruction 

 of either "fat-soluble A" or "water-soluble B." Since the ex- 

 periments were made upon rats, they would, of course, throw little 

 if any light upon the destruction of the antiscorbutic vitamine. 

 We plan to continue the study of the effects of heating upon the 

 vitamines in some of the staple articles of food. 



5 (1465) 



The rate of change of hereditary factors in Drosophila. 

 By H. J. Muller and E. Altenburg. 



[From the Rice Institute, Houston, Texas, and Columbia University, 



New York City.] 



A knowledge of the rate at which hereditary changes of various 

 sorts occur is the necessary groundwork for an adequate under- 

 standing of evolution. The wide recognition given to this fact 

 is attested to by the vast amount of literature on the subject of 

 "variation," but, with our new exact knowledge of the Mendelian 

 and chromosomal method of inheritance of the so-called "varia- 

 tions," it is evident that this literature has very little bearing on 

 the real question of how often changes in the hereditary factors, i.e., 

 mutations, actually occur: for the breeding procedures used in 

 the experiments there considered were not of the type necessary 

 for ferrctting out the new mutant factors as they arise, and 

 for distinguishing between them and the apparent variations 



