INHERITANCE 721 



The substances removed from solution were found not to exist in the 

 bodies of the animals. It appears, therefore, that the acclimatized animals 

 in some way destroy the injurious organic compounds. Presumably they 

 produce some secretion that has this effect. 



In the case of the inorganic poisons, arsenic and antimony, the acclima- 

 tized animals were found to have acquired the power to transform the 

 highly injurious trivalent compounds of the two elements into the rela- 

 tively harmless pentavalent compounds. 



The acclimatization was found to be, as a rule, specific for the substance 

 to which the animals had been exposed. Acclimatization to one of the 

 organic substances did not increase resistance to the other three. But in 

 the case of the related inorganic materials arsenic and antimony, acquire- 

 ment of increased resistance to one induced acclimatization to the other. 



INHERITED ENVIRONMENTAL MODIFICATIONS IN FORM AND STRUCTURE 



Reynolds (1923) and Jollos (1924) studied extensively the inherit- 

 ance of certain abnormal forms of the shell in Arcella; an extended review 

 of this work is given in the author's Genetics of the Protozoa (1929). 



The work of Jollos shows that these abnormalities are favored by 

 certain environmental conditions, and perhaps makes it probable that 

 they originate as environmental modifications. Inheritance of the abnor- 

 mal conditions continued for many generations. 



By selection, the grades or degrees of abnormality could be changed. 

 By long selection of the most nearly normal individuals, a stock that was 

 nearly or quite normal could be produced. According to Jollos, the length 

 of time required to bring the animals by selection back to a normal con- 

 dition is proportional to the length of time that the ancestors have lived 

 under the environmental conditions that favor the abnormality. 



When the abnormal stock is allowed to multiply without selection, 

 the proportion of individuals with but slight degrees of abnormality 

 increases. Jollos holds that this indicates that the abnormal condition is 

 essentially transient, a Dauermodifkation, in which the cytoplasmic 

 tendency to abnormality is in time overcome by the nuclear tendency 

 toward normality. On the other hand, the higher degrees of abnormality 

 are harmful to the organism, so that natural selection tends to weed these 

 out, causing the stock to become less abnormal in later generations. See 

 the extended presentation of the evidence and the discussion on this 



