viii BLOOD-STREAM: MOVEMENT IN VESSELS 245 



was placed in direct connection with the artery. This is Hiirthle's 

 rubber manometer. Since the rubber membrane easily perishes, 

 Gad substituted for it a thin metal plate. Finally, v. Frey 

 gave the most practical form and shape to the entire apparatus, 

 combining the maximum of sensitiveness with stability and 

 permanence. He called it a metal tonograph (Fig. 93). 



More recently (1904) Ducceschi has described a still simpler 

 method, by which the tracings of the normal blood pressure in the 

 carotid of dogs and rabbits can be recorded. After isolating a 

 sufficiently long tract of this artery in the neck, he divided it 

 between two ligatures, putting the central end in direct com- 

 munication with the isotonic lever of a myograph by means of an 

 inextensible thread, and counterbalancing the tension with an 

 adequate weight. In principle this method is the same as that 

 employed by En- 

 gelmann to record 

 the pulsations of 

 the frog's heart 

 (see next chapter), 

 and its author gave 

 it the name of 

 method of suspen- 

 sion of the artery, 

 just as Engelinann 



a 1 1 a rl Vie fVck T?IQ. 93. Von Frey's metal tonograph. in which the rubber membrane 



is replaced by a metal plate. 



method of suspen- 

 sion of the heart. It is evident that the pressure of the blood, 

 exerted on the closed trunk of the carotid, must distend it in 

 correspondence with the average pressure 1 ancL the rhythmical 

 oscillations due to the rhythmical beat of the heart (longitudinal 

 locomotion and arterial pulse). 



Since these methods all involve the opening of an artery, and 

 introduction of a cannula, they are only practicable on man in 

 certain surgical operations (amputations) and other conditions 

 more or less removed from a physiological state. Methods have 

 accordingly been invented by which it is possible to determine 

 blood pressure without any surgical operation, and these can 

 therefore be applied to man. Vierordt (1855) was the first who 

 conceived the idea of measuring the blood pressure in an artery 

 indirectly, by ascertaining the weight required to suppress the 

 pulsations. Waldenburg, Potain, Talma, Roy and Brown 

 attempted the solution of the same problem. The sphygmomano- 

 meter of v. Basch (1876) is a small instrument designed for this 

 purpose, which has found wide acceptance with clinicians on 

 account of its easy applicability. It consists of a rubber finger- 

 stall filled with water, by which the radial or temporal artery is 

 compressed. The finger-stall communicates by a rubber tube with 



