674 ABSORPTION. 



nated. But its insertion at D has another advantage. By the mode 

 in which the current from J towards S unites with that from V towards 

 S, a certain degree of diminished pressure must exist at D ; so that the 

 atmospheric pressure, on the surface of the water in the vessel B, will 

 be exerted in propelling it forwards. In the progress, then, of the 

 chyle and lymph along the thoracic duct, not only may the traction of 

 the more forcible stream along the veins draw the fluid in the thoracic 

 duct along with it, but, owing to the diminished pressure at the mouth 

 of the duct, atmospheric pressure may have some although probably 

 but little influence, in forcing the chyle and lymph from the chylife- 

 rous and lymphatic radicles onwards. The lymphatic glands have been 

 looked upon as small hearts for the propulsion of lymph ; and Malpighi 

 accounts for the greater number in the groin in this way; the lymph 

 having to ascend to the thoracic duct against gravity: and this appears 

 to have been somewhat the opinion of Bichat. There seems, however, 

 to be nothing in their structure that ought to lead to this belief; and, 

 if it be not muscular or contractile, it is manifest, that their number 

 must have the effect of retarding rather than accelerating the flow. 

 The most prevalent sentiment is, that they are somehow concerned in 

 the admixture of the lymph ; and by many it is conceived, that some 

 kind of elaboration is effected by them ; but, on this topic, we have 

 only conjectures. Of their true functions we know nothing definite. 



On the subject of the moving powers of the lymph, M. Adelon 1 has 

 remarked, that if we admit it to be the serous portion of the blood; 

 and that the lymphatics are vessels of return, as the veins are, the 

 heart might be considered to have the same influence over lymphatic, 

 that it has been presumed to have over venous, circulation; and whether 

 we admit this or not, as the thoracic duct opens into the subclavian 

 vein, .the influence of the suction power of the organ on the venous 

 blood may affect the progression of the chyle also. It cannot, how- 

 ever, as Muller 2 remarks, be the primary cause of the motion of the 

 chyle, for Autenrieth, Tiedemann, and Carus observed, when a liga- 

 ture was applied to the thoracic duct, that the part of the duct below 

 the ligature became distended even to bursting. We shall see here- 

 after, that during inspiration, absorption, it is imagined, may be facili- 

 tated by the dilatation of the chest, and the necessary diminution of 

 pressure on the heart and great vessels. 



Professor Miiller 3 discovered, that the frog, and several other am- 

 phibious animals, are provided with large receptacles for lymph, situate 

 immediately under the skin, and, like the heart, exhibiting distinct and 

 regular pulsations. The use of these lymph hearts appears to be to 

 propel the lymph along the lymphatics. In the frog, four of them, 

 have been found; two posterior, behind the joint of the hip; and two 

 anterior, on each side of the transverse process of the third vertebra, 

 and under the posterior extremity of the scapula. The pulsations of 



1 Art. Absorption, in Dict.de Medecine, 2de edit., i. 239, Paris, 1832; and Physiologic 

 de 1'Homrae, edit, cit., iii. 92. 



2 Handbuch, u. s. w.; and Baly's translation, p. 284, Lond., 1838. 



3 Philos. Transact, for 1833; and op. cit. See, also, his Observations on the Lymphatic 

 Hearts of Tortoises, in Muller's Archiv., Heft 1, 1840. 



