SUGGESTIONS FOR LABORATORY WORK 615 



fashion that a portion of the web is in the field. Study the field 

 with the low power. 



Note the rate and character of the blood flow in different ves- 

 sels. The larger vessels are either arteries or veins. In arteries the 

 blood flow is intermittent, and the rate of pulsation agrees with 

 that of the heart-beat. In veins the flow is more or less steady. 

 The smallest vessels are capillaries. These communicate, in 

 general, between arteries and veins. In the frog's web, however, 

 the circulation is anastomosing. In such a circulation some cap- 

 illaries can be seen connecting one vein with another. The direc- 

 tion of flow in anastomosing capillaries is sometimes forward, and 

 sometimes backward. 



Study a region showing arteries, veins, and typical, non-anas- 

 tomosing capillaries. 



THE CIRCULATION OF BLOOD IN MAN 



Pulse Tracings. To obtain a graphic record of the pulse the pres- 

 sure changes in the beating artery are transmitted to a delicate 

 recording device known as a tambour. For the transmitter a 

 thistle tube, with sheet rubber tied tightly, without stretching, 

 over the mouth, may be used. Secure a bone or wood button to 

 the center of the rubber. Connect the transmitter with the re- 

 corder by a rubber tube. Insert in the course of this tube a glass 

 T with a short rubber tube on the side neck. 



Gently press the button on the transmitter on the front surface 

 of the wrist directly over the point where the pulse can be felt in 

 the radial artery. The carotid artery in the neck may be used if 

 preferred. When the system is made air tight by closing the side 

 tube the tambour lever should pulsate in synchronism with the 

 artery. Obtain a record of these pulsations on a drum moving at 

 moderate speed. The notch in the descending limb, of the pulse 

 curve marks the closing of the semilunar valves, and therefore 

 the end of systole. 



Determinations of Pulse Rate. In these determinations two stu- 

 dents should alternate as subject and observer. Trustworthy 

 readings cannot be made upon oneself. The pulse should be 

 taken by pressing the tips of three fingers against the radial artery 

 at the wrist. Do not use the thumb. 



