100 



THE MECHANISM OF THE CIRCULATION. 



are also very small, the error due to the momentum of the mass is inappre- 

 ciable. Buisson 1 experimentally proved that the instrument is free from any 

 swing of its own. 



If a small mirror 2 be fastened over the radial artery, and a beam of light 

 thrown upon the mirror, the excursion of the pulse can be photographed on a 

 moving sensitised plate. If a small puncture be made in an artery, the jet of 

 blood can be brought to play on a sheet of white paper moved by clock- 

 work, and a hsemautograph can be thus obtained. 3 Both these methods yield 

 exactly the same type of curve as the Marey sphygmograph. The in- 

 strument has been modified in many ways. Dudgeon has constructed a less 

 cumbersome and more convenient form, suitable for the obtaining of clinical 

 records. 



These sphygmographs are less suitable for taking continuous records during 

 long periods of observation. For this purpose air transmission is employed, 

 and the pulse trace is obtained by means of a receiving and a recording 

 tambour. 



The frequency of the pulse. If for a space of twenty -four hours a 

 man be kept in bed, perfectly quiet, uniformly covered with clothes, 

 and without food, it will be found that the variations of the pulse rate 

 during the day are very small. Such variations as arise are due to 

 changes in temperature. Much clothing increases the frequency, while 

 exposure to cold lowers it. The variation due to the change of clothing 

 may be as much as ten beats per minute. 4 



The hot room of a Turkish bath greatly increases the pulse rate. In 

 an air-chamber at 65 C., the heart may attain to a frequency of 

 160 per minute. In the tropics the pulse of a traveller quickens, while 

 in the arctic regions it becomes slower. Drinking hot water accelerates 

 the pulse, while the imbibing of a large quantity of cold water slows it. 

 Every sensation of warmth, pressure, or discomfort in the stomach 

 accelerates the heart. The taking of cold foods does not alter the rate, 

 but hot meals increase it by as much as ten per minute. The heart lies 

 in apposition to the stomach, warmth increases the rapidity of the 

 heart ; and we may therefore assume that the warm food in the stomach 

 directly raises the excitability of the rhythmic mechanism of the 

 heart. The effect of meals on the pulse rate is shown in the following 

 example : 5 



1 Marey, "La circulation du sang," Paris, 1881, p. 217. 



2 Czermak, Mtzungsb. d. k. ATcad. d. JFissensch., math.-naturw. CL, Wien, 1863, Bd. 

 xlvii. Abth. 2, S. 438. 



3 Landois, Arch. f. d. ges. Physiol., Bonn, 1874, Bd. ix. S. 71. 



4 Bleuler and Lehmann, Arch. f. Hyg., Munchen u. Leipzig, 1888, Bd. iii. S. 224-231. 

 6 Adapted from Tigerstedt, "Physiol. des Kreislaufes." Leipzig, 1893, S. 27. 



