THE CIRCULATION OF THE BLOOD 



99 



(5) Is the effect clearly marked on the pressure tracing? 



(6) In the case of which nerve is the influence of stimulation the 

 more pronounced? 



(7) In one animal cut both vagi nerves end note the influence on 

 blood pressure for a period of one hour after the section. 



(8) In another animal cut both cardiac sympathetic nerves and 

 note the influence on blood pressure. 



FIG. 55 



XII. THE BLOOD PRESSURE IN THE TISSUES. 

 A. To Determine Capillary Blood Pressure. 



1. Appliances. A set of metric weights from 1 to 100 grams; 

 a common-sized watch-crystal; a f-inch round cover-glass, No. 3; 

 sealing-wax; linen thread; dividers; millimetre scale. 



2. Preparation. To make an apparatus for determining capillary 

 pressure mark upon the edges of the watch-crystal and cover-glass, 

 points distant from each other 120 of 



arc, cut three equal pieces of thread from 

 10 to 12 cm. in length; fasten the ends to 

 the points marked in the circumference 

 of the glasses with melted sealing-wax. If 

 the threads are of equal length, and if the 

 cover-glass is held in a horizontal plane, 

 the watch-crystal suspended by the threads 

 should be parallel to the cover-glass, and, 

 therefore, in an horizontal plane. If the 

 cover-glass is given a half-turn to right or 

 left, the three threads will cross as seen in 

 Fig. 55. A thread should be tied around 

 where this cross occurs and the knot se- 

 cured with sealing-wax. Weigh this ap- 

 paratus and mark upon the watch-glass 

 its weight in grams. 



Hold the left hand with palm upward, 

 fingers slightly flexed. Hold the apparatus 

 with the cover-glass horizontal and place 

 the middle of the cover-glass on the tip 

 of the ring finger, the watch-crystal 

 hanging below. The weight suspended 

 on the finger would be simply the weight of the apparatus. 



3. Observations. Place sufficient weight upon the watch-glass 

 scale-pan to nearly exclude capillary circulation from the flattened 

 circular area where the cover-glass presses upon the finger. If the 

 capillary circulation is completely excluded from this area the skin 



Apparatus for determining the 

 capillary pressure. 



