276 THE CIRCULATION OF THE BLOOD 



blood-pressure will fall rapidly, the heart-rate will become slower but 

 does not cease for a long time after respirations stop. 



Should a clot form in the cannula, put a bulldog forceps on the artery, 

 disconnect the manometer tube, and wash the clot out by a stream of 

 liquid from the pressure bottle. Use care not to allow this fluid to enter 

 the exposed wound. 



Represent the results of each individual experiment in the above series 

 in tabulated form which shall show: i, the blood-pressure and heart-rate 

 just before each experiment; 2, during the experiment; and 3, at different 

 times after the experiment until the normal is reached. After the data 

 are taken from the tracings and arranged in tabular form, make a study 

 of these facts and draw all the conclusions you can concerning the nervous 

 regulations of the heart and of the blood-pressure. Make a written report. 



2 2 . The Vaso-motor Changes in the Finger, the Plethysmogram. Insert 

 the ringer in the Porter ringer plethysmograph, fill the tube with warmed 

 water, and connect it with a small-sized air tambour. The variations in 

 volume of the finger are slight, so that one must use a most delicate 

 recorder. Take a tracing at a slow speed, i mm. per second. The finger 

 and its plethysmograph should be suspended so that no mechanical 

 movements will destroy the accuracy of the record. Observations through 

 several minutes will usually show variations in volume of the finger, 

 which will be recorded by the tambour. The reagent must be warm 

 and relaxed. 



Try a short mental problem. Cold air or cold water in the face will 

 usually be marked by a decrease in volume indicating vaso-constriction. 

 Warmth will lead to increase in volume indicating vaso-dilatation. In 

 sleep there is the greatest relaxation and a large volume pulse will be 

 present. 



23. The Vaso-motors of the Frog's Web. Prepare a frog for observa- 

 tion of the circulation of the web under the microscope, as described above, 

 giving it 3 drops of ether, or just enough i per cent, curare to destroy 

 voluntary movements. Quickly dissect the sciatic nerve in the thigh, 

 using extreme care not to interfere with the circulation. Mount the 

 preparation, pick out an active field of capillaries, small arteries, and 

 veins under the low power of the microscope, then adjust the high power 

 to a field which shows one or more small arteries. Make a drawing to 

 record the diameter of these arteries, using pigment cells for land-marks, 

 or measure with an ocular micrometer. Now quickly stimulate the 

 exposed sciatic nerve while keeping the selected artery under constant 

 observation. After stimulation for 10 seconds the diameter of the vessels 

 will be seen to decrease considerably, sometimes to the point of complete 

 occlusion. When the stimulation ceases, the vessel will remain contracted 

 for a few seconds, then will slowly regain its usual caliber, figure 201. 



