56 PHYSIOLOGY. 



3. Four inches of the same size glass tubing, for making connec- 

 tions. 



4. Several nozzles, made of the same size glass tubing, all fine, but 

 of varying degrees of fineness. 



5. India-rubber tubing, twelve feet, three eighths of an inch inside 

 diameter. This should be black, pure gum, rubber which is more 

 highly elastic than the other kinds. 



6. Three feet of rubber tubing, same size as above. 



7. Four inches of white rubber tubing, same size as above, for 

 making connections. 



In all the experiments, have one of the students assist by holding 

 the outlet tube, so that (i) all the members of the class may see the 

 stream, and (2) that the stream may be suitably directed, as into a pail 

 or sink. 



Count aloud, to mark the exact time of each compression of the 

 bulb, so the students can compare this with the time and duration of 

 the jets of water. 



Be very careful to use perfectly clean water, as any fine particles of 

 sediment drawn into the tube are likely to clog the fine outlet of the 

 nozzle. And it is well to take the further precaution not to let the 

 supply tube touch the bottom of the water-supply dish, as some fine 

 sediment may get in in spite of previous care. 



EXPERIMENT i . Remove the nozzle of the syringe, and put in its 

 place the long glass tube. Work the syringe, and note that the jet is 

 jerky, following each contraction of the bulb. 



EXPERIMENT 2. Substitute the rubber tube, three feet long, for 

 the glass tube. On working the bulb the stream will be found inter- 

 mittent. 



EXPERIMENT 3. Take off the rubber tube and replace the glass 

 tube, adding the nozzle. Here the pressure will be so great that it is 

 likely to push off the nozzle unless the assistant holds it firmly. It 

 could be tied on, but this takes more time. On working the bulb, 

 greater effort must be made on account of the resistance caused by the 

 narrower outlet. 



EXPERIMENT 4. Once more substitute the rubber tube, this time 

 with a glass nozzle in its end. Now, on working the bulb, resistance 

 will be felt, and the stream will be constant, or nearly so, and will con- 

 tinue for some time when the bulb is no longer worked. This is be- 

 cause the rubber has been stretched, chiefly laterally, and is now 



