ELEMENTARY VITAL PHENOMENA 181 



to show that for various reasons they ought not to be regarded as 

 demonstrative. Hence, thus far, the question is not decided. A 

 decision can be reached only by experiment, but not by such 

 experiments as those performed upon mice. It is a priori 

 improbable in the highest degree that injuries of the tail, the 

 finger, or similar parts of the body are inherited, for it is hardly 

 to be imagined that the organs in question stand in such a 

 relation to the sexual cells, through which alone reproduction 

 and inheritance occur, that their mutilation shall exercise a 

 marked influence upon those cells, which is the first requisite of 

 inheritance. In future experiments, therefore, mutilations must 

 be performed upon such organs as stand demonstrably in 

 correlation with the sexual organs, for only then would there be 

 the possibility of hereditary transmission. Few such correlations, 

 however, are known. In man, as is known, the development of 

 the larynx is correlated with that of the sexual organs. Men who 

 in their youth have lost the testes by castration retain throughout 

 life a larynx retarded in its development and a high childish voice. 

 The splendid sopranos in St. Peter's at Rome, whose artistic sing- 

 ing is so attractive, have often afforded examples of this. Similar 

 correlations ought first of all to be fully investigated and then 

 to be employed for experiment, unless experimentation is to be 

 a mere groping-about without plan, a process that leaves the 

 decision to chance. That influences which affect the germ-cells, 

 the ovum and the spermatozoon, influence the further develop- 

 ment in a high degree, is a priori clear, and, moreover, has recently 

 been shown, especially by the brothers Hertwig ('87), in a large 

 number of striking experiments. If, now, mutilations that alter 

 the germ-cells could be performed upon highly developed animals 

 or upon plants, it would be possible to decide experimentally 

 whether mutilations as such are transmitted by means of a 

 definite action upon the germ-cells, or whether they influence 

 the latter only in so far that offspring coming from those cells 

 have other defects and abnormalities that are not like the mutila- 

 tions. In the first case, there would be a real transmission of 

 acquired characteristics, in the second not. Hence the question 

 of the inheritance of acquired characteristics remains to be decided 

 experimentally. Whatever has thus far appeared upon either the 

 affirmative or the negative side is nothing but more or less 

 probable supposition. 



Special characteristics are not necessarily inherited. But the 

 general characters of every organism which for generations have 

 been reproduced constantly, whether they are exclusively innate 

 or are really acquired at some time by some predecessor, are 

 constantly transmitted in their essentials. A change takes place 

 so slowly that it can scarcely be perceived within the few genera- 

 tions that come under observation during the life of one man or of 



