Its Formation and Movement Lymph

An objection to these views has been raised on the ground that it is difficult to see how pressure of tissue fluid can be transferred to lymph capillaries. These vessels should collapse if the pressure of the fluid outside them were greater than that inside. An ob servation, however, made long ago by Gaskell enables one to see how this relationship can occur. He noticed in the epiglottis that fine fibres of an elastic nature passed from the lymph vessels into the surrounding tissue, so that if the latter became swollen with fluid, these fibres were pulled on and helped to keep open the lumen of the vessel to which they were attached.

Arterial Pulsation.

In some situations the lymph vessels form sheaths round the arteries. In these it is obvious that arterial pulsation will have a tendency to propel the lymph f or wards. The beating of the aorta assists in this forward movement by rhythmical compression of the thoracic duct where it passes behind that artery. The influence of this factor can be seen espe cially well in the flow from a thoracic duct canula in an animal which is breathing very slowly.

Respiration.

If the lymph rising into a thoracic duct canula is observed it is seen to issue most rapidly during expiration. During inspiration the external pressure on the thoracic duct is lessened and so the pressure within it becomes less than that in the vessels of the abdomen. There is thus a tendency for the lymph to flow from the abdomen into the thoracic duct. At the same time as this suction action occurs, the diaphragm is con tracting and descending to increase the intra-abdominal pressure so that lymph is also actively pushed from the abdominal vessels into the thoracic duct.

Thus, during inspiration the thoracic duct is completely filled. During expiration the reverse phenomenon occurs, the pressure on the walls of the distended thoracic duct is increased, and, owing to the presence of valves, the lymph is forced out from the duct into the canula, or, in conditions of normal life, into the venous system. According to Lee, normal respiration is capable of rais ing the pressure in the thoracic duct to about II mm.Hg. while excessive breathing will raise it to as much as 26 mm.Hg.

Intrinsic Forces.

The foregoing description of the forces in volved applies to mammals such as man or dog. In some types of animal, however, such as fish, amphibia, reptiles and birds special contractile sacs have been developed which have the function of actively propelling the lymph into the venous system by means of rhythmical beats. These "lymph hearts" have disappeared from mammals, but two species, the rat and guinea pig, and ac cording to some the mouse, possess mesenteric lymphatic vessels which are rhythmically contractile throughout their course and actively propel the lymph forward. In the guinea pig rhythmi

cally contracting vessels have also been seen on the pleural sur face of the diaphragm. Similar vessels in several species have been examined, but under the conditions of experiments have not been seen contracting rhythmically. Nevertheless, these vessels are actively contractile to certain stimuli and are supplied with nerves, the stimulation of which causes contraction and, accord ing to some, dilatation as well. Dogiel states that the innervation extends even to the lymph capillaries.

From the foregoing observations one concludes that the con traction of the vessel walls themselves is a factor in the propul sion of lymph. That such contraction does occur at some time seems to be undeniable, but the requisite physiological conditions have so far escaped detection.

BIBLIOGRAPHY.-Richet's Dictionaire de Physiologie, Lymphe (la formation et la circulation de la), with full list of references to work on all aspects of the lymphatic system ; R. Meyer-Bisch and F. Gunther, "Physiologie und Pathologie der Lymphbildung," Ergeb. d. Physiol. (1926), vol. xxv. (with a good bibliography of the more modern literature) ; A. Effinger, "Die Bildung der Lymphe," Ergebnisse der Physiologie (1902), 1 Jahrg. Biochemie ; E. Owerton, "Ueber den Mechanismus der Resorption u. der Secretion"and "Ueber die Bildung u. Resorption der Lymphe"; Nagel's Handb. d. Biochemic. vol. iii., 2e Halite. 206; E. H. Starling, "The production and absorp tion of Lymph," Textbook of Physiology, Schafer vol. i. 285-311 (1898).

Some of the More Important Papers.—E. H. Starling, "Contribution to Physiology of Lymph secretion" Journ. Physiol. 14. 131 (1893). "The influence of Mechanical Factors on Lymph production," ibid. 1894. 16. 224. "On the mode of action of Lymphagogus," ibid. 1894-95. L. Asher and W. Gies, "Untersuchung fiber die Eigenschaften und die Entstehung der Lymphe," Zeit. f. Biol. 1900. 22. 180. W. Cohnstein, "Ueber die Theorie der Lymphbildung," Arch. f. d. ges. Physiol. 1896. 63. 587. R. Heidenhain, "Versuche u. Fragen zur Lehre von der Lymphbildung," Arch. f. d. ges. Physiol. 1891. 49. 2°9. H. J. Ham burger, "Zur Lehre der Lymphbildung," Arch. de Physiol. 1895. 364. Bainbridge, "The lymph flow from the submaxillary gland," Journ. Physiol. 190o. 25. XVI. L. Asher and A. G. Barbera, "Untersuchung fiber die Eigenschaften u. d. Entstehung der Lymphe," Zeit. f. Biol.

1898. 18. 454. (H. W. F.)