20 STUDIES IN PHYSIOLOGY. 



unchanged in shape? Do any granules pass from one cell to the 

 next one? Where is the motion fastest? 



While the observations are in progress, be careful not to allow 

 the preparation to become dry : add a little water occasionally, 

 and note whether the rate of motion is increased or diminished 

 for the next minute or so. 



(d) Questions to be answered by experiment. (1) What effect 

 upon the rate of protoplasmic movement does increase of tem- 

 perature produce? 



In order to keep the slide with the specimen, prepared as 

 above, from touching the metallic stage of the microscope, place 

 under each end of it a piece of thick pasteboard, and then clamp 

 it down firmly by means of the stage-clips, so that it cannot 

 be easily displaced. After the slide has been in position for a 

 few minutes, note the rate of movement of the granules at the 

 ordinary temperature of the room. When this has been accu- 

 rately determined, place near the specimen, on the slide, a coin 

 or other small piece of metal which has been heated to 40 C., 

 and note the change of rate. Afterwards apply more and more 

 heat 03* a second and a third application of the coin, heated each 

 time higher by immersion in hot water, and note the result. Of 

 course this very simple method of experiment does not allow one 

 to determine the exact temperature to which the specimen is 

 heated, but its temperature is only a little lower than that of the 

 coin. 



For exact experiments employ the apparatus described in 

 557 or 558. 



(2) What effect upon the rate of movement does a decrease of 

 temperature cause? 



Prepare a fresh specimen as directed under (6), lower the tem- 

 perature of the slide by the application of a coin which has been 

 immersed in ice-water, and note all changes in the rate of move- 

 ment. Still lower temperatures are easily secured by placing in 

 a small copper cup on the slide (an ordinary copper cartridge- 

 shell answers very well) a mixture of ice and salt. 



If in either of the preceding experiments the motion of the 

 granules has been arrested, endeavor, b}- reversing the applica- 

 tion, to re-establish movement : thus, if the movement was ar- 

 rested at the higher temperature, apply cold ; if it was arrested by 

 cold, apply heat. 



