252 



PHYSIOLOGY 



CHAP. 



muscles of the latter, especially the bkvps, are entirely relaxed. With one 

 hand the operator feels the bradiial m- radial pulse at the bend of the elbow 

 joint, and with the other he slowly blows in air, until every trace of pulse is 

 lost. If the manometer scale is now read for the exact point at which the 

 pulse disappeared without reappearing during maintenance of the pressure, 

 the desired pressure A'alue will be obtained. 



Another simple apparatus, easy to handle, which with certain modifica- 

 tions is making its way like the preceding into medical practice, is Gartner's 

 tonometer (1899). This apparatus (Fig. 98) to some extent combines the 

 principles of the methods of Hiirthle and of Riva-Rocci. It also consists of 

 a hollow ring, with an internal wall of rubber, which can be gradually 

 inflated by an elastic spray bellows, and communicates on the other hand 

 with a mercury manometer, on the scale of which the pressure values may be 



read. It is fixed round one of the 

 fingers, and measures the total 

 pressure of the blood in the arteries 

 of that finger. The method is as 

 follows. First, as in Hiirthle's 

 method, the phalanx of the finger 

 to be experimented on is made 

 anaemic, by applying an elastic 

 bandage to the finger or by slipping 

 a rubber ring over it ; or, on the 

 principle of an Esmarch's bandage, 

 rolling down from the point of the 

 finger to the root, over the differ- 

 ent joints in succession, a fine 

 strip or tube of, elastic rubber. 

 The finger is then introduced into 

 the pneumatic ring of the appara- 

 tus, so that the ring embraces the 

 phalanx, and air is blown in from 

 the elastic bag by turning the screw 

 of the compressor until the pres- 

 sure of the tonometer exceeds that 

 of the blood. The bandage which 

 FIG. 93. Gartner's tonometer. Consists of bellows produced anaemia is then removed, 



(i) or screw compressor with an elastic d th pressure w ithill the tono- 



bag, communicating on the one hand with , i , , 



a one-armed mercury manometer (m), on meter Slowly reduced by turning 



the other with a hollow rin<; () which slips t ne SC rew that compresses the elas- 



tic bag in the opposite direction, 

 until the internal pressure exceeds 

 the external counter-pressure, and the blood, re-enters the arteries of the 

 finger as shown by the flushing of the pulp, or subjectively by the return of 

 the pulse. The value read at that moment on the manometer scale is equal 

 to the total pressure of the blood in the digital arteries. 



V. Volkmann concluded from the data which he collected in 

 order to determine the variations of normal blood pressure in 

 various species of animals, that the height of pressure is in no 

 sort of ratio with the size of the animal. The lateral pressure in 

 the dog's aorta, e.g., fluctuates between 130 and 180 mm. Hg, in 

 the rabbit between 100 and 130 mm. Hg, in the horse between 

 150 and 200 mm. Hg. This seems paradoxical at first sight, but 

 is not so when we reflect that the work of the heart depends not 

 only upon the magnitude of resistance or pressure, but also upon 



