178 THE ACTION OF THE LIVING CELL 



duction of offspring having a higher natural resistance 

 than is ordinarily the case. This conclusion is not 

 based upon the experiments just cited alone, for re- 

 sults of a similar and even more striking nature have 

 been obtained with mice, rats, and guinea pigs as well. 

 Before considering these in detail, it is worth while 

 to outline the probable relation between the health 

 of the mother and that of her offspring. 



It is now generally accepted by biologists that ac- 

 quired characteristics of the parents cannot be in- 

 herited by their offspring. This conclusion is based 

 upon the results of thousands of experiments in this 

 direction which have been made since the beginnings 

 of scientific biology. While from time to time appar- 

 ent evidence to the contrary has been recorded in the 

 literature, subsequent investigation has in each case 

 proved such evidence to be the result of either faulty 

 experimentation or observation. Further, the modern 

 theory of heredity, which has withstood innumerable 

 onslaughts, furnishes an adequate basis for the non- 

 inheritance of acquired characters. According to pres- 

 ent day concepts, an animal's inheritance is uniquely 

 determined by the genes passed on through the germ 

 plasm from one generation to another. So far as is now 

 known, an organism's inheritance can be modified 

 only by factors capable of altering such genes. To 

 date, the only known method of accomplishing this is 

 by means of the X-ray which, as Muller (1925) has 

 shown, may cause such alterations in the genes as to 

 lead to the formation of mutants. Such being the case, 

 it appears obvious that ordinary factors affecting the 

 activities and health of the parents can in no wise influ- 

 ence the inheritance of the offspring. 



