THE RATE OF BLOOD FLOW 



187 



the sudden propulsion of blood into the aorta ; at c is the predicrotic 

 wave, and at d the dicrotic wave. 



This piece of tracing must also be compared with that given in 

 fig. 146, which was obtained from a dog, using Fick's kymograph. 



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Fig. 150. — Normal Blood Pressure and Respira- 

 tion. Rabbit. Hurthle Manometer. 



Both tracings show precisely the same points, 

 and further show that by employing these 

 instruments we are able to record even the 

 smallest and most transient variations in pres- 

 sure. 



In connection with the consideration of the 

 blood flow the student should examine the con- 

 struction of the following piece of apparatus whose 

 aim is to enable us to determine the rate of flow of 

 the blood along a vessel. Ludwig's stromuhr 

 (fig. 151) consists of two glass bulbs, a and b, which 

 communicate with each other above, and below 

 are fitted into a circular brass base, P, revolving 

 on a lower frame, e. Through this frame are two 

 channels, opening respectively at c and d. By 

 means of two stops the revolving disc p is checked 

 in the two positions, so that either a or B can be 

 brought into communication with the tube at c. The opposite bulb then 

 opens out at o. The method of employing the apparatus is to fill the bulb a 

 with oil and the bulb b with defibrinated blood. The tube c is then connected 

 to the central end of the artery the rate of flow of the blood along which we 

 wish to determine, and d is tied into its peripheral end. At an instant which 

 is recorded the blood from the artery is allowed to flow into a. The oil rises 

 on the surface of the blood, and the upper orifice of the bulbs being closed it 

 forces the defibrinated blood from B into the peripheral end of the vessel. 

 As soon as a is filled with blood the bulbs are rapidly rotated, so that the bulb 

 B comes to occupy that position previously held by a. The bulb n now con- 

 tains the oil, and more blood entering it from the artery, the oil is once more 



C ■""■■ l "™" 



I'm. 151. — Lui>wih> 



Stbomtjhe. 



