THE BLOOD-PRESSURE MODEL 271 



Anesthetize a cat or dog with a chloroform-ether mixture, tie it on the 

 animal-holder and, when the eye reflexes are lost, expose the jugular vein 

 on the right side, the carotid artery and the jugular vein on the left. Fill a 

 2-cm. hypodermic syringe with i per cent, methylene blue in physiological 

 saline, insert the needle into the right jugular vein, pointing it toward the 

 heart. Lift the left carotid artery and place under it a strip of moist white 

 paper 2 cm. wide; prepare the left jugular vein in the same way. Place the 

 animal so that these vessels are lighted to the best advantage. At a given 

 moment inject the contents of the hypodermic syringe, noting the time 

 with a stop-watch. Observe the color of the left carotid and the left 

 jugular, respectively, very carefully, and take the time of the first appear- 

 ance of the methylene blue. The color will appear first in the artery, 

 second in the vein. The difference in time between the moment of injec- 

 tion and the moment of color in the artery represents, with a slight cor- 

 rection, the circulation time of the pulmonary or lesser circulation. The 

 time from the injection until the color in the other 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. 



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

 apparatus, which illustrates all mechanical parts involved, has been 

 arranged by Porter, 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, (a) 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; (b) the influence 

 on these two pressures when the rate is increased, when it is decreased, 

 (c) the effect on these pressures when the peripheral resistance is great, 

 when it is low. With a sphygmograph, (d) 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: (e) The character and rate of the outflow when water 

 is pumped into the rigid glass tube with no resistance to the outflow; (f) 

 when 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, (g) Pump the 

 water into a rubber tube of smaller size and compare with the proceeding 

 when there is no resistance to the outflow; also (/?) when a glass tube of 



