EFFECT OF TEMPERATURE ON ANIMAL TISSUES. 43 



In order to determine whether similar structural changes, as 

 have already been described in the cases of Stcntor and Monas, 

 could be produced on other forms as well, the low temperature 

 experiments have been continued on many other Protozoa, both 

 Infusoiia and Rhizopoda, and in all of them changes identical with 

 those described above have been obtained. Monas is the only 

 form in which it has been found possible to control the formation 

 of spores, but in all the others resting cells were formed at the 

 low temperature, which reverted to the motile condition when 

 restored to the normal temperature. 



I. THE REVERSAL OF VITAL PHENOMENA BY A REDUCTION 



OF THE TEMPERATURE. 



The results of these low-temperature experiments on the Pro- 

 tozoa suggested an interesting comparison to the experiment of 

 Loeb's, 1 in which the tentacles and polyps of a Campanularian 

 Hydroid were reduced to the undifferentiated protoplasm of the 

 stolon by bringing them in contact with some foreign substance. 

 It appeared that for the Protozoa a lowering of the temperature 

 as well as a contact stimulus brings about just such a reversal of 

 the vital phenomena until the undifferentiated resting cell is 

 formed, while a small increase in temperature accelerates the met- 

 abolic processes. To see if a lowering of the temperature brought 

 about similar changes in the more complex multicellular animals 

 a series of experiments was begun on the fresh-water Hydra. 



It was at once observed that whenever a Hydra is exposed to 

 a temperature of 4 to 6 C., the tentacles gradually become 

 shorter and thicker, and are finally completely absorbed into the 

 body. As the absorption goes on, the ectoderm and entoderm 

 cells of the tentacles lose their individuality and form an undif- 

 ferentiated mass of protoplasm, which is slowly taken into the 

 body of the Hydra (see Fig. 4). The tentacleless body of the 

 Hydra becomes slowly resolved into a dense spherical mass of 

 coagulated protoplasm, in which no distinction between the in- 

 dividual cells can be made out, and remains in this condition as 

 long as it is kept at a low temperature (see Fig. 3), but quickly 

 forms tentacles and a double layer of cells again when it is re- 



1 Loeb : American Journal of Ph ysiology, 1900. //". , p. 178. 



