THE ARTERIAL PULSE 259 



stop-watch. Observe the color of the left carotid and the left jugular, respect- 

 ively, very carefully, and take the time when the first appearance of the 

 methylene blue is noted. The color will appear first in the artery, second 

 in the vein. The difference in time between the moment of injection and 

 the moment of color in the artery represents, with a slight correction, the 

 circulation time of the pulmonary or lesser circulation. The time from the 

 injection until the color in the jugular vein represents the total time of 

 circulation. 



Stewart has made these determinations even more correctly by the elec- 

 trical-resistance method. He injected 10 per cent, salt solution and deter- 

 mined the variation in resistance by a galvanometer. If the galvanometer is 

 available, then check the above determinations by the electrical method, 

 arranging the apparatus under the direction of an instructor. 



14. The Blood-pressure Model. An artificial model of the circulatory 

 apparatus, which illustrates all mechanical parts involved, has been arranged 

 by Porter. Other forms, which show these as well, are usually available 

 or can be easily constructed. The model should have the following 

 possibilities: A pump, which permits of rhythmic action at a varying rate 

 and varying force; a resistance to the outflow liquid which can be increased 

 or decreased; and an elastic set of vessels into which the pump discharges. 



If Porter's schema is used, determine the following points: The pressure 

 in terms of mercury in the arterial and venous limbs of the apparatus when 

 the pump makes a rate of 72 per minute; the influence on these two pressures 

 when the rate is increased, when it is decreased; the effect on these pressures 

 when the peripheral resistance is great, when it is low. If a sphygmograph 

 is available, take a tracing of the pulse in the elastic tube representing the 

 arterial side of the schema. 



If an ordinary bulb syringe and simple apparatus is used, then deter- 

 mine the following: The character and rate of the outflow when water is 

 pumped into the rigid glass tube with no resistance to the outflow; w r hen a 

 glass tube of smaller caliber is connected with the end of the larger glass 

 tube so as to produce a high resistance to the outflow. Pump the water into 

 a rubber tube of smaller size and compare with the proceeding in which 

 there is no resistance to the outflow; also when a glass tube of small caliber 

 is introduced into the end in order to produce high resistance to the outflow. 

 Determine the amount of resistance necessary to produce a constant outflow 

 when the pump has a rate of 72 beats per minute. In this experiment what 

 effect is produced on the outflow if the rate of the pump is varied ? if the force 

 of the stroke is varied? if the elasticity of the rubber tube representing the 

 artery is varied ? If the resistance represented by the size of the glass tube 

 at the outflow is varied ? 



15. The Arterial Pulse. The form of the arterial pulse may be taken 

 by one of the various sphygmographs applied to the radial artery at the 



