REACTIONS TO HEAT AXD COLD. 



II 



in principle to that of Mendelssohn, but more easily constructed and 

 permitting exact observation of the organisms with the microscope, 

 though otherwise much less elegant than Mendelssohn's. This ap- 

 paratus is shown in Fig. 5. It consists essentially of three glass tubes, 

 of 8 millimeters bore, which are supported in a horizontal position, 

 side by side, by passing them through auger holes in a block of 

 wood. The tubes are one inch apart and are placed exactly at 

 the same level, so that a glass slide rests equally on all three. To 

 the two ends of each of these rubber tubes are attached. The rubber 

 tubes from one end pass upward into vessels of water raised on a shelt 

 above the level of the apparatus. From the other end the rubber tubes 



pass downward into a waste pail, thus acting as overflow tubes. A 

 trough, or slide (5), containing infusoria, is placed on the three glass 

 tubes ; the water in the vessels on the shelf is heated or cooled to any 

 desired temperature, and is then siphoned off and allowed to flow 

 downward through the glass tubes. The rate of flow is controlled by 

 pinchcocks. In this manner heated water can be caused to flow 

 beneath one end of the slide, cold water beneath the other. The slide 

 being thus unequally warmed, the reactions of the organisms can be 

 observed. The rubber tubes leading from the hot and cold vessels can 

 be interchanged, so that the temperature at either end or the middle of 

 the slide can be at once changed and made high or low, without the 



* FIG. 5. Apparatus used for testing reaction to heat and cold. For de- 

 scription, see text. 



