HEREDITY AND HUMAN IMPROVEMENT 371 



tinuity of the germ plasm, or the transmission of a part 

 of the germinal substance relatively unchanged. A part 

 of the original germ plasm of the fertilized ovum differ- 

 entiates into the bodily organs, while a part remains 

 comparatively unchanged and forms the basis from which 

 the new individual may arise. Parent and offspring 

 resemble one another because both sprang from a com- 

 mon substance. Germ plasm comes from preceding 

 germ plasm, the bodies of organisms being the carriers 

 of this substance, or as Gal ton .says the " trustees of the 

 germ plasm." Since it has become customary to look 

 upon inheritance as coming not from the bodies of parents 

 but from germ cells of which the body is both the product 

 and the carrier, many biologists think that the character- 

 istics acquired by the body are not transmissible to the 

 next generation. It was formerly held that those char- 

 acters which an organism acquires by its own efforts or 

 through the action of the environment were in a measure 

 passed on to its offspring. It was thought that if a black- 

 smith strengthened his arm by wielding the hammer his 

 son would have a stronger arm as a result of his father's 

 exercise. But the majority of biologists now doubt if 

 such acquired characters as the increased or decreased 

 development of a particular part are ever transmitted. 

 Numerous mutilations such as cutting off the tails of 

 mice have been practised for many generations without 

 producing the slightest effect upon the offspring, and 

 certainly the decorative mutilations which many savages 

 have indulged in for untold generations such as gashing 

 the cheek, flattening the skull or deforming the lips, noses, 

 ears or feet have not had the least influence on the children 

 of these peoples who are born as free from blemishes as 

 those of civilized man. The transmission of acquired 

 characters is a subject on which numerous experiments 



