308 THE THEORY OF THE GENE 



along with other individuals normal in appearance. In 

 later generations abnormals continued to appear, but 

 only from certain individuals. 



If we examine the pedigrees of the alcoholic series 

 there is no evidence that the results conform to any of 

 the known Mendelian ratios. Moreover, the varied locali- 

 zation of the effects shown by the abnormals is not of a 

 kind that resembles what we meet with when single gene- 

 changes are involved. On the other hand, the defects have 

 many points of resemblance to the kind of changes that 

 we are familiar with in experimental embryology when 

 abnormal development is brought about by treating eggs 

 with toxic agents. Stockard has called attention to these 

 relations, and interprets his result to mean that an injury 

 of some sort to the germ-cells has been produced by the 

 alcohol — an injury to some part of the machinery that is 

 involved in heredity. The effects are localized only in so 

 far as they pertain to those parts of the body that are 

 most sensitive to any departure from the normal course 

 of development. These parts are most frequently the 

 nervous system and the sense organs. 



More recently Little and Bagg have carried out a series 

 of experiments on the effects of radium on pregnant mice 

 and rats. When the treatment is properly administered, 

 the young mice in utero may develop abnormally. When 

 examined before birth many of them show hemorrhagic 

 areas (Fig. 156) in the brain and cord, or elsewhere 

 (especially in the leg rudiments). Some of these embryos 

 die before parturition, and are absorbed, others are 

 aborted. Still others are born alive and some of these sur- 

 vive and may procreate. The offspring often show serious 

 defects in the brain or in the appendages. One or both 

 eves mav be defective. Both eves may be absent, or one 

 only may be present, much reduced in size. Bagg has bred 

 some of these mice and finds that they produce many 



