GENETIC VARIATIONS 349 



and peculiarities which are found to be due to gene muta- 

 tions. The same types of mutations are produced by heat as 

 occur spontaneously and under radiation; they are inherited 

 in the same manner. 



Certain other matters of great interest have been re- 

 ported by Goldschmidt and Jollos in connection with the 

 mutations induced by heat. In some of their experimental 

 cultures very great numbers of mutations were produced. 

 It was reported by these authors that the heat produces 

 changes in the bodies of the individuals subjected to the 

 heat, and that in later generations similar inherited changes 

 appear as a result of gene mutations. However these later 

 mutations did not as a rule appear in the descendants of the 

 particular individuals that had been directly changed by the 

 heat. 



In the continuation of this work by Jollos, a further rela- 

 tion, of the very greatest interest, is reported. Subjection of 

 one generation to a high temperature causes a slight in- 

 herited effect, due to a slight mutation of a particular gene. 

 Subjection of those changed descendants to the high tem- 

 perature for another generation is reported to increase the 

 effect and alter the gene still more. By continued subjection 

 to high temperatures for many generations a series of 

 gradations is thus produced, each one hereditary at ordinary 

 temperatures, but passing from slight changes in earlier gen- 

 erations to very great ones in later generations. Thus, in 

 one series of experiments, a certain gene was so altered, 

 in the first generation subjected to heat, as to cause a slight 

 darkening of the body color. Subjection to heat in later 

 generations Increased the effect on this gene until finally 

 the body was black. In another series, the red color of the 

 eye was, by subjection of successive generations to heat, 

 caused to become lighter and lighter until It was yellowish, 

 and until finally entirely white eyes were produced. The mu- 

 tations to which these changes In eye-color were due were all 



