500 



CIRCULATION OF BLOOD AND LYMPH. 



arteries and veins, it is assumed that the animal is in a recumbent 

 posture. In an animal standing upon his feet, especially in 

 an upright animal like man, it is obvious that the effect of 

 gravity will modify greatly the actual figures of pressure. Upon 

 the arteries and veins of the feet, for example, there will be 

 exerted a hydrostatic pressure equal to the height of the column 

 of liquid between the feet and the heart, which adds itself to the 

 pressure resulting from the circulation as caused by the heart. 

 When the animal is in a recumbent position the hydrostatic fac- 

 tor practically disappears. (See p. 515.) 



d 



Fig. 201. Figure of the Riva-Rocci apparatus (Sahli) : a. The leather collar with 

 inside rubber bag to go on the arm; c, the bulb for blowing up the rubber bag and thus 

 compressing the artery; d, the manometer dipping into the reservoir of mercury, 6, to meas- 

 sure the amount of pressure. 



The Method of Determining Blood-pressure in the Large 

 Arteries of Man. It is a matter of interest and practical impor- 

 tance to ascertain even approximately the arterial pressure in man 

 and its variations in health and disease. The first practical method 

 for determining this point upon man was suggested by von Basch 

 (1887), who devised an instrument for this purpose, the sphygmo- 

 manometer. Since that time a number of different instruments 

 have been described, but attention may be called to two only, which 

 illustrate sufficiently well the principles involved. In the first 

 place, it must be clearly recognized that the arterial pressure in 

 the large arteries of man shows marked variations with the heart 

 beat; the pressure during the beat of the heart rises suddenly 

 to a much higher level than during the diastole. The relation of 

 the systolic (or maximum) and diastolic (or minimum) pressures 

 is indicated by the diagram in Fig. 195. The instruments that 

 have been invented for determining human blood-pressure are in 



