278 ELLINOR HELENE BEHRE. 



upon these and other phases of the subject by many other later 

 investigators. The general conclusions on the direct effect of 

 temperature may be summed up in the words of Verworn (1899) : 

 "Within certain limits increasing temperature acts to augment 

 vital processes. Up to a certain point excitation increases with 

 increase of temperature. This holds good for very different 

 phenomena and for very different forms of living substance." 



But the phenomenon of acclimation to temperature changes, 

 while well known, has not been submitted to extensive analysis. 

 It has been observed of course that in warm springs organisms 

 are found, living at temperatures as high as 85 C. (Flourens, 

 1846), or even 98 C. (Ehrenberg, 1859), closely related to species 

 which live in water seldom as high as 40 C. Acclimation to 

 temperature has also been observed in Euglena, where Schwartz 

 (1884) and Aderhold (1888), working separately, found that 

 Euglena collected in summer are not active below 5 or 6 C., 

 in winter at as low as O C. No explanation for this phenomenon 

 is offered and no further experiments have been performed upon 

 this material. But Dallinger (1880) found that flagellates will 

 endure a rise of temperature from 15.6 C. to 70 C. if the 

 change is very gradual. And both Schottelius (1867) and 

 Dieudonne (1894) succeeded in causing bacilli which normally 

 produced a fluorescing pigment and trimethylamine at 22 and 

 not at 35, to produce these substances at 35 if kept at that 

 temperature through a sufficient number of generations. 



The most complete and elaborate experiments on vertebrates 

 are those of Davenport and Castle (1895) upon Bufo tadpoles, 

 and those of Loeb and Wasteneys (1912) upon Fundulus. Dav- 

 enport and Castle found that Bufo tadpoles kept at 15 went into 

 heat rigor at 40.3 C., from which state recovery was possible; 

 but those kept at 25 C. for 28 days resisted this higher tempera- 

 ture perfectly, going into heat rigor only at 43.5. If brought 

 back to 15 for 17 days they lost their resistance to high tempera- 

 ture, but only partially, going into heat rigor now at 41.6 C. 

 The Fundulus experiments of Loeb and Wasteneys showed similar 

 results. Fish from a temperature of 10 C. die in less than two 

 hours at 29 C., and in a few minutes at 35 C. ; but if first exposed 

 to 27 C. for 40 hours they can live indefinitely at 35 C., and 



