380 ADAPTIVE VARIATIONS. 



was found possible to raise the temperature of the or- 

 ganisms from 41.7 to 58.3. Also to raise the tem- 

 perature from 61.1 to 70.0 took only a few months 

 (number not stated). As to the absolute upper limit 

 of temperature these infusoria can withstand, it is of 

 course impossible to judge, but there seems no reason 

 to suppose that it might not be considerably higher 

 than that reached by Dallinger. A striking proof of 

 the altered condition of the organisms was furnished 

 by the fact that some of those acclimatised to 70.0, 

 died off when placed in a suitable nutritive solution at 

 15.6. 



This acclimatisation was probably for the most part 

 a direct adaptation of the protoplasm to its new en- 

 vironment, but it must also have been in part due 

 to natural selection. Dallinger noticed on more than 

 one occasion that a good many of the organisms were 

 killed off, and these would doubtless have been the less 

 adaptable ones, the more adaptable surviving. Still, 

 as far as one can judge from the brief account given, 

 the temperature was often raised over considerable in- 

 tervals without any such fatalities. 



Dallinger's results, in addition to their intrinsic 

 value, are of great interest in that they enable us to 

 account for the presence of various Protophyta, such as 

 Oscillatoricu and Nostocacecc in hot springs. The tem- 

 perature of many of these springs is considerably above 

 60.0 C., and that of the California geysers, in which 

 Nostocacecc (possibly Proiococcus) are found, reaches 

 the remarkable temperature of 93. Certain metazoa, 

 also, are stated to live at temperatures considerably 

 above 45, or temperatures which prove fatal to their 



