502 



CIRCULATION OF BLOOD AND LYMPH. 



Therefore to blanch this area would require a column of water contain- 

 ing 1000 c.mms. with a cross-area of 4 sq.mms. The height of this column 

 would therefore be equal to ^^ or 250 mms. of water, that is, 18.5 mms. 

 Hg. 



The results obtained by this method are not very constant and 

 can only be considered as approximate. It would appear, how- 

 ever, that the pressure lies somewhere between 20 and 40 mms. 

 of mercury. Thus, upon the gums of a rabbit von Kries found a 

 capillary pressure of 33 mms. Hg. 



By means of a more adjustable instrument von Reckling- 

 hausenf estimates that in man the pressure within the capil- 

 laries of the finger-tips or, to be more accurate, within the small 

 arteries supplying these capillaries, is equal to 55 mms. Hg. 

 (See p. 510.) 



The general relations of the pressures in arteries, veins, and 

 capillaries may be expressed in a curve such as is shown in Fig. 

 200. 



It should be added that in this curve and in all the figures 

 so far quoted in regard to the actual pressure within the different 



d 



Fig. 201. Figure of the Riva-Rocci apparatus (Sahl-i) : 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. 



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 arte- 

 ries and veins of the feet, for example, there will be exerted a 

 * Von Recklinghausen, "Archiv f. exp. Path. u. Pharmak.," 55, 375, 1907. 



