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ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



central side of the ligature, and that its distal end does not collapse 

 altogether, owing to the fact that the carotid arteries anastomose rather 

 freely with one another. Observe that the distal end of the vein is 

 highly distended, whereas its central end is collapsed. This is one of 

 the tests which Harvey employed to prove the circulation of the blood. 

 Observe the changes in the caliber of the vein during inspiration 

 and expiration. During the former period its size is decreased, and 

 during the latter, increased. These changes are referable to the aspira- 

 tory action of the thorax, because the inspiratory movement augments 

 the elastic pull of the lung tissue upon the yielding walls of the central 

 venous trunks. During expiration, on the other hand, the lung tissue 

 recoils more completely, and does not exert so powerful a traction upon 

 the venous trunks and their contents. Accordingly, the inspiratory 

 movement decreases the pressure in the central veins and draws a 

 larger quantity of blood into them and the right side of the heart. 



FIG. 65. SCHEMA ILLUSTRATING THE CAUSE AND VELOCITY OF THE ARTERIAL PULSE. 

 W, Basin with water; P, valved rubber bulb; B, band-tubing between the laterals C. 



Observe the changes in the caliber of the artery during inspiration 

 and expiration. It increases during the former period, and decreases 

 during the latter. Since the heart receives a larger quantity of blood 

 during inspiration, it is capable of transferring a larger amount of it 

 into the arteries. The pulmonary blood-vessels are at this time more 

 widely dilated, and permit a free through flow. 



Free the common carotid artery from its fascia and insert in it a 

 glass cannula. Fill the latter with a solution of sodium carbonate. 

 Fill the rubber tubing and central limb of the mercury manometer with 

 the same solution. Determine the zero-line or line of atmospheric 

 pressure (760 mm. Hg.). Connect the arterial cannula with the man- 

 ometer. 



Annotation. The zero-line is ascertained as follows: Bring the level of the mer- 

 cury in the central limb of the manometer on the same level with the carotid artery. 

 Connect the rubber tubing with a glass bulb filled half-way with a solution of sodium 

 carbonate. Adjust the level of this solution to the level of the mercury in the 

 central limb of the manometer. At this time the recording needle of the float, 



