I20 INTRODUCTION TO SEXUAL PHYSIOLOGY 



of Weismann and Cope, who cut of! the tails of mice for many 

 generations, were likewise negative, the offspring never being 

 born without tails or with their tails in any way abnormal. A 

 number of experiments by more recent investigators (such as 

 those of Payne who bred fifty generations of flies in total darkness 

 without impairing their reaction to light) have provided no 

 evidence of the transmission of acquired characters. 



There are certain other recent experiments in which positive 

 results are claimed, and of these Kammerer's and Pavloff's are 

 among the most notable. Kammerer found that black and yellow 

 salamanders became more black or more yellow, according as 

 they were placed on a black or yellow background, and that their 

 offspring raised on a neutral background showed some of the 

 effects produced on their parents. Kammerer also obtained 

 evidence of the transmission of colour changes in lizards as well 

 as of modifications in the breeding habits of the midwife toad, 

 and the development of horny pads on the digits of the male. 

 The interpretation, however, has been disputed, and Morgan 

 and others regard the evidence as utterly inadequate. Pavloft''s 

 experiments were upon mice, but have not yet been described in 

 full. As related they appear to constitute the strongest evidence 

 as yet presented of the inheritance of an acquired character, and 

 they are all the more remarkable in that they relate to a con- 

 ditioned reflex, a very high form of nervous activity. The mice 

 w^ere trained to run to their feeding place on the ringing of a bell, 

 and the first generation required 300 lessons, that is to say, 

 it was necessary to combine the feeding with the bell ringing for 

 300 times in order to accustom the mice to run to the feeding 

 place on hearing the bell ring. The second generation, however, 

 needed only 100 lessons, while the third generation required fifty, 

 the fourth ten, and the fifth as few as five lessons. This result 

 is remarkable, but the experiments require confirmation before 

 the conclusions reached can be unequivocally accepted. 



In all the experiments so far referred to, the question before 

 the investigator has been as to whether acquired characters or 

 the effects of use or disuse are inherited specifically. In other 

 cases the evidence is indicative rather of the inheritance of a 

 general effect. This is so with Stockard's experiments on 

 the influence of alcohol, and with those of Bagg and Hanson and 

 Little on the effects of radium or x-rays. With many of these 



