CIRCULATION. 437 



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 manoraetric 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 OP 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 

 minute 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 duct 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 

 received by the thoracic duct, which runs the whole length of the chest. 

 Both of the main ducts have walls which, relatively, are very thin ; and, like 

 the smaller lymphatics, the ducts are abundantly provided with valves so 

 disposed as to prevent any regurgitation of lymph from either duct into its 

 branches. Each duct terminates on one side of the root of the neck, where, 

 in man, the cavity of the duct joins by an open mouth the confluence of the 

 internal jugular and subclavian veins where they form the innominate vein. 

 At the opening of each duct into the vein a valve exists, which permits the 

 free entrance of lymph into the vein, but forbids the entrance of blood into 

 the duct. 



It is a peculiarity of the lymphatic system that soine of its vessels end and 



begin by open mouths in the so-called serous cavities of the body those vast 



irregular interstices between organs the membranous walls of which interstices 



are known as the peritoneum, the pleurae, and the like. For present purposes, 



1 M. von Frey : Die Untersuchung des Pulses, 1892, p. 35. 



