WATER RELATIONS IN HIBERNATION. 243 



the sixth generation at Tucson, have constantly the capacity to 

 hold onto the water content in their tissues, are more resistant 

 to desiccation, and in every way are different in their reactions 

 to the water loss than are the same materials that have lived at 

 Chicago continuously. In Fig. 2 I have plotted the results 

 of one of these dual tests made upon T 99 in the fourteenth 

 generation of its existence at Tucson, and the stock C 100 from 

 Chicago. 



The curve of response of the materials at Chicago shows a 

 rapid water loss in the first day, the onset of death from desicca- 

 tion by the end of the second, and the death of all in this test 

 at three and one half days, with the attainment of a constant 

 dry weight under the conditions at about the sixth day. In 

 the sample from Tucson, however, the curve of response to desic- 

 cation shows a much less rapid loss, the first deaths not occurring 

 until the seventh day and total death not until the twelfth day, 

 and dry weight constancy about the fifteenth, but not as low as in 

 the culture of Chicago materials. The temperature in this test 

 was constantly 20 C., the temperature used in all such testings. 



There is a very obvious difference in the ability of the two 

 sets of organisms to let go of the water in the tissues under- 

 desiccating conditions in the environment. In these tests the 

 conditions were most severe, with absolutely dry and rapid 

 passage of air, in all respects immensely more severe than are 

 ever obtained in any desert complex during hibernation, as the 

 animals are then protected in the ground and desiccation is 

 slow and gradual. However, the desert adjusted group shows 

 that it has the ability to hold the water, or less capacity to let 

 the water loose from its tissues when subjected to the pull of an 

 intensely dry environic condition, and this one difference would 

 decide the fate of either set of materials in different environments. 



The eliminations in the survival tests made at Chicago of the 

 samples from the Tucson stocks, are clearly due to their not being 

 able to let go of the water in their tissues with sufficient rapidity 

 to keep the freezing point below the temperature of the soil, 

 consequently they are actually frozen by the decreasing tempera- 

 tures accompanying the onset of the northern winter, and exam- 

 ination of test cultures made for the purpose at Chicago shows 



