220 INTRODUCTION TO GENERAL PHYSIOLOGY 



jet into the end of C. Immerse the end of K in a bowl of water. 

 With the clamp E widely open, compress A gently with the hand 

 at regular intervals of about one or two seconds. Air will first be 

 driven out and then water, which will escape from the end of C in 

 spurts. Gradually close E, continuing the regular squeezing of the 

 bulb as before. The spurts will be converted into a more or less 

 constant stream. 



Remove the jet and connect up again to F. Open the screw 

 clamp and pump water through until all air is driven out, and then 

 slip on, under water, the connection between G and K. 



Periodic compression of A will be seen to cause the valve B to 

 open, K to close. On releasing the pressure the suction of the bulb 

 draws water through K, while B closes. The mercury in both 

 manometers oscillates greatly, while the mean pressure in D is not 

 much higher than in H (vaso-dilatation). Close next the screw 

 clamp gradually. Note the rise in D and the nearly complete 

 cessation of oscillations in H (vaso-constriction). If G is only 

 partially distended at rest, owing to the amount of water in the 

 system being insufficient to fill it, it will be noticed that when 

 the compressions are started, particularly with a high resistance 

 at E, G becomes less full. The arterial tube is stretched by the high 

 pressure. 



After running in more water under pressure through L, it can 

 be shown that a higher arterial pressure is maintained with a similar 

 degree of compression of A. 



Take away the manometer H with its T-tube and connect up 

 the tubes at the gap. Insert the T-tube between E and F. Pump- 

 ing as before, note that the pressure beyond E is low when the screw 

 clip is narrowed. Next insert the manometer D between F and L, 

 and notice that there is not much difference of pressure between 

 the two ends of the capillary region, but that if E is widened both 

 pressures rise, thus indicating a rise in the capillary pressure. 



Restore the manometers to their original positions. Arrange 

 that G is well filled, pump regularly and then compress G with the 

 hand, continuing the pumping as before. Decrease of the capacity 

 of the system raises the arterial pressure. 



It will facilitate the more accurate comparison of pressures if 

 the compression of A is arranged to be done by a piece of wood, 

 attached at one end by a hinge to the base of the board on which 

 the system is fitted. This piece of wood passes over A, resting 

 upon it. The free end, when pressed down, meets a stop of such 

 a height as to give an appropriate degree of compression to A. This 

 stop may be a long screw passing through the wooden base. 

 The rate of the compression is kept constant by the beat of a 

 metronome. 



