10 



EXPERIMENTAL PHYSIOLOGY 



ling. If the glass 'cools too soon return it to the flame and 

 treat as before. 



B. Cutting. Wet the file and, holding the tube firmly 

 with finger and thumb, make a slight scratch across it. 

 Turn the tube over and repeat the operation at a point 

 directly opposite. Now grasp the tube in both hands, one 

 on each side of the scratches, and bend sharply. The result 

 should be a clean, square-ended break. The edges may be 

 rounded by holding them in the flame a moment. 



II. COLLECTION OF GASES (OPTIONAL). 



Apparatus. Pneumatic trough and support, glass tube bent at 

 right angles, large-mouthed bottles, piece of glass to cover mouth of 

 bottle. 



Directions. A. Fill the trough with water to the depth 



of a half inch above the 

 top of the support. Fill 

 the bottle with water, 

 cover the mouth with 

 the glass, and invert, 

 putting the mouth under 

 the water of the trough. 

 Remove the piece of 

 glass, and place the bot- 

 tle over one of the 

 holes of the support. 

 Does the water flow out? 

 Explain. 



Now introduce the 



FIG. 2. 



short end of the glass 

 tube into the mouth of the bottle (see Fig. 2) and blow 



