314 HEREDITARY ADAPTATION TO HIGHER TEMPERATURE 



experiments which apparently showed some such result. In the 

 bacteria and other unicellular organisms, there is no doubt that 

 cultures may be adapted to very marked changes both in temperature 

 and concentration of toxic substances. This is, however, analogous 

 to the adaptation of an individual multicellular organism, and cannot 

 be considered hereditary in the sense in which the word is used in 

 regard to higher organisms. The individual cells of a bacterial culture 

 bear the same relation to each other as the somatic cells of a single 

 multicellular organism, and are not at all analogous to successive 

 generations of individuals of multicellular organisms. 



The experiments reported in this paper were made with aseptic 

 cultures of Drosophila. These are especially favorable for such a study 

 for the following reasons. (1) If kept free from microorganisms the 

 results of any experiments made with them become quite regular. 



(2) They have a very short generation time, about 7 days at 30°. 



(3) Loeb and Wasteneys ^ found that the individual Drosophila show 

 the same marked adaptation to temperature as does Fundulus. In 

 the case of the latter, Loeb and Wasteneys found that fish transferred 

 suddenly from 10 to 35°C. died in the course of 1 to 2 hours, whereas 

 fish transferred first to 27° for 2 or 3 days and then put at 35° were 

 able to live indefinitely at this temperature. The results with 

 Drosophila showed equally striking individual adaptations.'^ These 

 experiments were partially repeated and confirmed in the course of 

 the present work. 



The relation of the rate of growth and of the duration of life of 

 Drosophila to the temperature has been the subject of a previous 

 paper from this laboratory.^ It was found in that work that the 

 insects developed normally up to a temperature of 32.5°C. Above 

 this temperature the pupal stage was injured and no further develop- 

 ment took place; but the larval and imago stages could live at a 

 temperature several degrees higher. It was also found that increasing 

 the temperature from 10 to 27.5°C. increased the rate of development of 

 the larvae and pupae; but that between the temperatures of 27.5 and 

 32°C. the rate decreased again; i.e., the larvae grow more slowly at 



^ Loeb, J., and Wasteneys, H., J. Exp. Zool., 1912, xii, 543. 



^ Loeb, J., and Wasteneys, H., unpublished data. 



' Loeb, J., and Northrop, J. H., J. Biol. Chem., 1917, xxxii, 103. 



