210 HANDBOOK OF PHYSIOLOGY. 



177. It consists of a hollow Ospring, filled with fluid, the interior of 

 which is made to communicate with the artery by means of a flexible 

 metal tube and canula. In response to the pressure, transmitted to 

 its interior, the spring tends to straighten itself, and the movement 

 thus produced is communicated by means of a lever to a writing style 

 nnd so to a recording apparatus. This instrument obviates the errors 

 which might be caused by the inertia of the mercury in the mercurial 

 manometer; it also shows in more detail the variations of the blood 

 pressure in the vessel during and after each individual beat of the heart. 



Fig. 176. A form of Pick's Spring Kymograph, a, Tube to be connected with artery: c hollow 

 spring, the movement of which moves b, the writing lever; e, screw to regulate height of b- d out- 

 side protective spring; g, screw to fix on the u right of the support. 



In fig. ] 78 is seen a tracing taken with Tick's Kymograph from an 

 artery of a dog. 



As regards the actual amount of blood pressure, from observations 

 which have been made by means of the mercurial manometer, it has % 

 been found that the pressure of blood in the carotid of a rabbit is capa- % 

 ble of supporting a column of 2 to 3.5 inches (50 to 90 mm.) of mercury, 

 in the dog 4 to 7 inches (100 to 175 mm.), in the horse 5 to 8 inches 

 (152 to 200 mm.), and in man the pressure is estimated to be about the 



same. 



To measure the absolute amount of this pressure in any artery, it is 

 necessary merely to multiply the area of its transverse section by the 

 height of the column of mercury which is already known to be sup- 



