80 EXPERIMENTS WITH BLOOD-FLOW. 



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

 inch inside diameter. This should be black, pure gum, rubber 

 AY Inch is more highly elastic than the other kinds. 



G. 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 (1) 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 1. 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 intermittent. 



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 assis- 

 tant 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 



