SOME PROBLEMS IN THE PHYSIOLOGY OF THE PROTOZOA 295 



after which, with further decrease in temperature, cold rigor and 

 death ensue. In spite of these limitations, however, the Protozoa 

 have the power of adaptation to high temperatures on the one hand, 

 and low temperatures on the other. Ehrenberg cites the presence of 

 Nassnla, Enchelys, and AmpJiileptus in the waters of the Ischian hot 

 springs, which reach a temperature far above the normal for most 

 Ciliata and Flagellidia, while the presence of H&matococcus on high 

 mountains and in polar regions, or of various Flagellidia in frozen 

 pools, is common knowledge. The maximum temperature for com- 

 mon Flagellidia varies usually between 40 and 50 C. (Schultze, '63 ; 

 Strasburger, '78; Klebs, '83), although Dallinger cites a number of 

 common forms which live until 60 is reached, while the spores of 

 these forms withstand temperatures far beyond the boiling point. 

 With Rhizopoda, the maximum temperature seems to be somewhat 

 less than with Flagellidia. Kiihne ('64) found the maximum for 

 Amoeba difflnens and Actinospharium at 45 C., and similar results 

 were obtained by Schultze ('63) and Vervvorn ('89). 



The Ciliata also have a generally lower maximum temperature than 

 do the Flagellidia, although important exceptions are found where, by 

 adaptation to new conditions, the organisms are able to withstand a 

 considerable temperature. The common forms stand a temperature 

 of from 38 to 42 C., and the activity of the cilia resembles that of 

 ciliated epithelium described by Engelmann ('79). According to 

 Rossbach's description of the increase of heat upon the activity of the 

 ciliate Stylonychia, 4 marks the lower limit of motion when the animal 

 is nearly at rest, above 25 the movements become violent, although 

 still spontaneous and normal, while from 30 to 35 the motion 

 becomes uncertain and the animals lose their power of direction, a 

 condition which gives place to a violent rotation about the axis until 

 death finally ensues. In connection with the general stimulation of 

 the body by heat, there is frequently a definite movement of the 

 organism toward or away from the source of the stimulus (thermo- 

 taxis). This seems to have been first observed by Stahl ('84) in con- 

 nection with the plasmodia of dSt/ialtum septicum. He placed a strip 

 of filter paper, upon which a plasmodium had flowed, between two 

 beakers in such a way that one end of the plasmodium lay in cold 

 water (7), while the other lay in warm water (30). The streaming 

 of the plasm began at once toward the warmer water until the plas- 

 modium was completely immersed, although previously the movement 

 had been in the opposite direction. Verworn ('89) observed a similar 

 thermotactic phenomenon in Amoeba Umax, while, more recently, 

 Mendelssohn ('95) has shown that, in the Ciliata, Paramoecium seeks 

 warmer water in temperatures below 24 to 28, while in temperatures 

 above this the reverse reaction takes place. 



