LESSON XIX 

 THE CIRCULATION (Continued) 



THE CAUSE AND VELOCITY OF THE PULSE. DIRECT METHOD OF 

 ASCERTAINING THE BLOOD-PRESSURE 



1. Schema Illustrating the Differences in the Velocity of the Blood 

 Flow. Procure a glass bulb, such as is represented in Fig. 64. Con- 

 nect its inlet tube by means of a relatively narrow glass tube with the 

 water hydrant. On opening the stop-cock the 



water will advance to a higher level, its flow 

 being most rapid in the narrow inlet tube, very 

 slow in the enlarged central portion, and inter- 

 mediate in the outlet tube. If all the arteries, 

 capillaries, and veins could be united into single 

 tubes, the calibers of these three divisions would 

 differ in the same way, i. e., the bed formed by 

 the arteries would be the smallest of all, and 

 that of the capillaries the largest. Since the 

 speed of flow is inversely proportional to the 

 lumen of the vessel, the blood must attain its 

 greatest velocity in the arteries, and its slightest 

 velocity in the capillaries. 



2. Schema Illustrating the Cause and Velocity 

 of the Pulse. Procure four glass tubes, each 

 about 1 m. in length and 1 cm. in diameter. 

 Arrange them vertically about 20 cm. apart, 

 and connect them in series by means of band- 

 tubing, each piece being about 50 cm. in length. 

 Attach a valved rubber bulb to the end of this 

 system, and allow its inlet tube to dip into 

 a basin filled with water. Compress the bulb 



rhythmically until this entire system has been well filled. The water 

 then rises in the laterals to a certain level, indicating the pressure ex- 

 isting at these different points. Secondly, each compression of the bulb 

 then produces an oscillation of the water in the successive laterals, the 

 water in the lateral nearest the rubber bulb being moved first (Fig. 65) . 



3. The Direct Method of Determining the Arterial Blood-pressure. 

 Weigh the animal and compute the quantity of blood present in its 

 body. Give it ether and maintain the anesthesia until it has been killed. 

 Perform tracheotomy. Expose the carotid artery on the left side and 

 the external jugular vein on the right side. (See Lesson X.) Place a 

 silk thread loosely around each blood-vessel. Raise both sufficiently to 

 occlude them. Notice that the artery is more highly distended on the 



103 



FIG. 64. SCHEMA 

 ILLUSTRATING THE DIF- 

 FERENCE IN THE VELOC- 

 ITY OF THE BLOOD FLOW. 

 A, Arteries; C, cap- 

 illaries; V, veins. 



