126 LYMPHATIC SYSTEM. 



The coats of lymphatic vessels have, in common with all 

 other parts of the body, arteries and veins for their nourish- 

 ment ; this is rendered probable by their being susceptible of 

 inflammation, for they are frequently found in the form of a 

 cord, painful to the touch, and extending from an ulcer to the 

 next lymphatic gland, instances of which are mentioned below. 1 

 These painful swellings of lymphatic vessels likewise show that 

 their coats have sensibility, and therefore that they have nerves 

 as well as arteries and veins. 



The lymphatic system in most animals, but particularly in 

 man and quadrupeds, is full of valves. These valves have been 

 painted by the celebrated Nuck, Ruysch, and others, and are 

 much more frequent than in the common veins, and thence 

 these lymphatics have sometimes been distinguished by the 

 name of valvular lymphatic vessels. Those valves are gene- 

 rally two in number, are of a semilunar shape, and the one is 

 sometimes much larger than the other. In most parts of the 

 body these valves are so numerous that there are three or four 

 pair in an inch of space, but sometimes there is no more than 

 one pair. They are less numerous in the thoracic duct than in 

 the branches of the system ; thence it might be supposed that, 

 in proportion as we go from the trunk to the branches, we 

 should find them thicker set ; but this is not always true, for 

 I have observed them more numerous in the lymphatic vessels of 

 the thigh than in those of the leg. When the vessels are dis- 

 tended with lymph they appear larger where the valves are, 

 which sometimes gives a lymphatic vessel an appearance of 



1 Chapter xiii. 



lyrj 



sels contract powerfully in the necks of living dogs. In horses and 

 dogs killed during digestion, I have several times seen the lacteals well 

 distended ; and yet contracting so fast in the course of less than an hour, 

 as to become nearly or completely empty. Miiller's b discovery of pul- 

 sating sacs connected with the lymphatic cavities of frogs, is now well 

 known ; and similar lymphatic hearts, as they are called, have since 

 been observed, containing lymph and connected with the lymphatic 

 vessels, in reptiles generally and in birds. See Dr. Jos. J. Allison's 

 paper, in the American Journ. Med. Sc. Aug. 1838 ; and Mr. Paget's 

 Report in the Brit, and For. Med. Rev. vol. xix, p. 2/9. 



* History of the Absorbent System, p. h Physiology, tr. by Dr. Baly, vol. i, 

 27, 4to, Loud. 1784. p. 274. 



