98 THE CELL 



20 C.; 2-4 seconds at 26 C.; T5 seconds at 31 C.; and '65 seconds 

 at 37 C. From these figures it is apparent that " each consecu- 

 tive degree of temperature produces a corresponding slight 

 acceleration " (Nageli, Velten). 



Finally, it is necessary to mention the remarkable behaviour of 

 protoplasm towards sudden great fluctuations of temperature, and 

 also towards partial or uneven heating. 



Fluctuations of temperature may be either positive or negative, 

 that is to say, they may be caused by a raising or a lowering of 

 temperature. The consequence of a violent thermal stimulation 

 is a temporary cessation of all movements. However, after a time, 

 the motion recommences at a rate corresponding to the tempera- 

 ture (Dutrochet, Hofmeister, de Vries). The accuracy of these 

 observations has been questioned by Velten (IV. 38). According 

 to his experiments, fluctuations of temperature between the neces- 

 sary limits produce neither a cessation nor a slackening of the 

 protoplasmic movements, which, on the contrary, immediately 

 proceed at a rate corresponding to the temperature which has 

 been attained. 



Stahl (IV. 35), in his experiments upon the plasmodia of 

 Myxomycetes, has made some very interesting discoveries concern- 

 ing the effects produced by partial heating. If a -portion of such 

 a plasmodium, which has spread its network out over an even 

 surface, be cooled, the protoplasm is seen to travel gradually from 

 the cooler to the warmer part, so that the one portion of the net- 

 work is seen to shrink up, whilst the -other becomes swollen. The 

 experiment may be conducted in the following manner: Two 

 beakers, one filled with water at 7, and the other with water at 

 30, are placed quite close to one another ; a wetted strip of paper 

 over which a plasmodium has spread itself is then placed over 

 their contingent edges, so that one of its ends dips into each 

 beaker ; the temperature of the water in the beakers is not allowed 

 to vary. After a time the plasmodium, by stretching out and 

 drawing in its protoplasmic thread, succeeds in creeping over to 

 the medium which is best adapted to it. 



No doubt most free-living protoplasmic bodies move somewhat 

 in this fashion, for as a rule their movements are regulated by 

 expediency, that is to say, they take place in order that the life of 

 the organism may be maintained. For instance, flowers of tan 

 sink down during the autumn to a depth of several feet into the 

 warmer layers of the tan, in order to pass the winter there. 



