236 Heredity and Environment 



ney found that rotifers poisoned with alcohol were weaker in 

 resistance to copper salts and were less fertile than others, and 

 when brought back to normal conditions the first generation was 

 weak but the second was normal. On the other hand Stockard 

 finds that the injurious effects of alcohol on guinea pigs persist 

 through two or more generations. In man alcohol may have an 

 "induction" effect on offspring, but fortunately it does not seem 

 to alter hereditary constitution. Probably of a similar character 

 are Sumner's results ; he found that mice raised in the cold have 

 shorter tails than those raised at higher temperatures and this 

 modified character appears in the next generation. If this is an 

 after effect or "induction'' it should disappear in the following 

 generations. 



Kammerer found that salamanders with black and yellow spots 

 when reared on yellow soil gradually lose their black color becom- 

 ing more yellow, and their young continue to grow more yellow 

 until finally almost all black may disappear. The offspring of 

 such salamanders are said to be more yellow than normal; but 

 this work has been called in question and needs confirmation. 

 Even if confirmed the result may be an after effect or "induction" 

 which would soon disappear under usual conditions, and there is 

 no evidence that it is really inherited. 



Such cases are not instances of true inheritance ; they do not 

 signify a change in the hereditary constitution but an influence on 

 the germ cells of a nutritive or chemical sort comparable with 

 what takes place when fat stains are fed to animals ; the eggs 

 of such animals are stained and the young which develop from 

 such eggs are also stained, though the germinal constitution re- 

 mains unchanged. The very fact that the changed condition is 

 reversible and that it disappears within a short time is evidence 

 that it is not really inherited. 



In conclusion : ( 1 ) Developed characters, whether "acquired" 

 or not, are never transmitted by heredity, and the hereditary con- 

 stitution of the germ is not changed by changes in such charac- 

 ters. (2) Possibly environmental stimuli acting upon germ cells 



