THE CIRCULATORY SYSTEM 



175 



spending to the strokes of the pump. While working the pump press 

 lightly with the finger on the rubber tubing of the arterial side ; a 

 distinct pulsation is felt with each stroke. Repeat the same on the 

 venous side. 



82. Osmosis. Prepare a dialyzer by tying a thin animal membrane 

 (sausage skins, to be obtained of a butcher, furnish excellent mem- 

 branes for osmosis) over one end of a small lamp chimney. Partly 

 fill the dialyzer with a strong solution of sugar and place it in a larger 

 vessel of pure water, so that the liquids in the two vessels are at the 

 same level. In a short time the contents of the dialyzer begin to rise, 

 owing to the greater flow toward the denser liquid. It will also be 

 found that the water in the outer vessel becomes sweet as osmosis 

 goes on. If the membrane is allowed to become thoroughly dry after 

 being tied on the dialyzer, osmosis goes on more rapidly. 



M N 



Fig. 98. Apparatus for illustrating the circulatory system. 



A bulb syringe, by which water is forced through the apparatus. 



B rubber tubing packed with bits of sponge to represent capillaries. 



C rubber tube connecting arterial and venous regions. When C is closed with 



the pinchcock the liquid must all pass through tubes B. 

 D small tube ending in capillary point and closed with a pinchcock. When 



open it allows arterial " spurting " to be demonstrated. 

 E tube which shows venous flow. It ends in a tube of small caliber in order 



to produce a venous pressure. 

 M, N manometers consisting of glass tubing bent in a U-shape and partly 



filled with mercury. They show the pressure applied to the arterial and 



venous sides respectively. 



