LESSON XVIII 

 THE CIRCULATION 



THE CAPILLARY CIRCULATION. CONVERSION OF AN INTERMITTENT 

 INTO A CONSTANT FLOW. SCHEMA OF THE CIRCULATION 



1. The Capillary Circulation. Procure a microscope with low- and 

 high-power objectives, a thin cork board about 20 cm. long and 10 cm. 

 wide, and a few pins. Bore a hole about 1 cm. in diameter close to 

 the margin of the cork board. Pith a frog, being careful not to lose 

 any blood. Immediately close the opening with the pointed end of a 

 short piece of wood. Place the frog, dorsum turned upward, upon the 

 board and bring one foot over the hole in the cork board. Stretch the 

 web uniting the second and third toes across the opening, and hold the 

 toes in place by means of pins or threads. Do not stretch the web 

 unduly, so as not to block the blood-vessels. Adjust the body of the 

 frog in an easy position. 



Fasten the cork board to the stage of the microscope and illuminate 

 the web under an objective of low power. Moisten the frog repeatedly 

 with saline solution. Observe the movement of the blood and differ- 

 entiate between the red and white corpuscles. Note the differences 

 in the caliber of the blood-vessels and the speed of the blood flow. 

 Ascertain whether a certain vessel is an arteriole, a true capillary, 

 or a venule. Select a true capillary and observe how the red cells force 

 their way through it, elongating if necessary. Find a capillary which is 

 so small that only plasma passes through it. Do you observe an inter- 

 mittency in the flow anywhere in the field? What is its probable cause? 

 Have you seen a reversion of the blood flow? Give its cause. 



Carefully adjust the high-power objective to the web, and repeat the 

 preceding observations. 



2. Intermittent, Remittent, and Constant Flow. Procure a piece of 

 band-tubing about 1.5 m. in length. Insert in one of its ends a glass 

 cannula, and in the other a valved rubber syringe. Dip the inlet tube 

 of the latter in a basin of water and ask the assistant to hold the end of 

 the band-tubing over the sink. 



Compress the rubber bulb at intervals of five seconds. Note that 

 the tubing fills gradually, but does not discharge until it has attained 

 a definite degree of distention. It then discharges a certain quantity 

 of water with every compression of the bulb (intermittent flow). Com- 

 press at a faster rate until the flow does not cease entirely during the 

 interims (remittent flow). Compress at still briefer intervals until 

 the tubing attains a high degree of distention and continues to empty 

 its contents evenly during the time when the rubber bulb aspirates 

 (constant flow). Obviously, the successive muscular efforts required to 



