CIR C ULA TIOX. 1 45 



already stated, however, the probabilities are in favor of the valvular origin 

 of the dicrotic wave. 



If it be true that the closure of the aortic valve causes the dicrotic wave, 

 the instant marked by the commencement of this wave, in the mauometric 

 trace inscribed by the pressure within the first part of the arch of the aorta 

 itself, practically marks the instant of closure of the aortic valve. We have 

 seen (p. 130) that this doctrine has been made use of in the elucidation of the 

 curve of the pressure within the ventricle. 



The Diagnostic Limitations of the SphygmogTam. — The feeling of 

 the pulse, imperfect as is the most skilled touch, cannot be replaced by the 

 use of the sphygmograph. The presence, between the cavity of the artery 

 and the surface of the body, of a quantity of tissue the amount and elasticity 

 of which differ in different people, and even differ over neighboring points of 

 the same artery, renders it impossible so to adjust the spring of the sphygmo- 

 graph as to be able to obtain a reliable base-line corresponding to the abscissa, 

 or line of atmospheric pressure, in the case of the manometric curve of blood- 

 pressure. The effects produced by slight differences in the placing of the 

 instrument tend to the same result. By the absence of such a base-line the 

 sphygmographic curve is shorn of quantitative value as a curve of blood- 

 pressure, and cannot give information as to whether, in clinical language, the 

 pulse be hard or soft, large or small. Nor can a long or short pulse be iden- 

 tified from the appearance of the sphygmogram. 1 The pulse-trace still 

 requires much elucidation ; but when further study shall have rendered 

 clearer the true extent, the normal variations, and the causes of the complex 

 and incessant oscillations of the walls of the arteries, it may well be believed 

 that both physiology and practical medicine will have gained an important 

 insight into the laws of the circulation of the blood. 



P. The Movement of the Lymph. 



The Lymphatic System. — The lymph is contained within the so-called 

 lymphatic system, the nature of which may be summarized as follows : 



The lymph appears first in innumerable minute irregular gaps in the tis- 

 sues, which gaps communicate in various ways with one another, and with 

 miuute lymphatic vessels, which latter, when traced onward from their begin- 

 nings, presently assume a structure comparable to that of narrow veins with 

 very delicate walls and extremely numerous valves. These valves open away 

 from the gaps of the tissues, as the valves of the veins open away from the 

 capillaries. The lymphatic vessels unite to form somewhat larger ones, each 

 of which, however, is of small calibre as compared with a vein of medium 

 size, until at length the entire system of vessels ends, by numerous openings, 

 in two main trunks of very unequal importance, the thoracic duet and the 

 right lymphatic duct. The latter is exceedingly short, and receives the ter- 

 minations of the lymphatics of a very limited portion of the body ; the termi- 

 nations of all the rest, including the lymphatics of the alimentary canal, are 



1 M. von Frey : /'"' Untersuehumg des Pulses, 1892, 8. 35. 

 Vol. I.— 10 



