278 ABSORPTION. [CHAP. xxvi. 



A lymphatic system exists in all the vertebrata, but the glands are wanting 

 in fishes and reptiles, and are very few in birds, being found only in the neck. 

 In fishes and reptiles, however, there occur large and intricate lymphatic 

 plexuses, chiefly without valves, accompanying and sometimes completely 

 surrounding the blood-vessels in a luxuriance quite superior to anything 

 found in the higher classes. Moreover, there exist in the lymphatic trunks 

 in these animals and in birds, pouches furnished with valves and muscular 

 walls, which contract rhythmically and urge on the lymph towards the veins. 

 These lymphatic hearts are, in birds at least, formed of the striped fibre, 

 according to the observation of Stannius ; and we owe to Volkmann the 

 interesting fact, that in frogs their contraction may be be excited by the 

 direct influence of portions of the spinal marrow.* 



Do the Lacteal and Lymphatic Vessels absorb f From the 

 account now given, it is clear, that the structure and arrangement 

 of the lymphatic vessels fit them only for the conveyance of fluid 

 in one direction, viz., from the various tissues in which they 

 originate to the great veins, and thence to the heart. Hence 

 there can be no doubt, that, whatever other function they may 

 subserve, they are designed to carry fluid into the blood either 

 from the exterior of the body, as in the case of the digestive 

 mucous membrane and the skin, or from the interstices of the 

 various textures, where it may have been derived either directly 

 from the circulating mass, or indirectly from the waste of the 

 textures themselves. It was till lately assumed too exclusively 

 that this system of vessels was the sole agent in such absorption, 

 and hence the name of absorbent system as applied to it, and the 

 view which allowed the blood vessels no share in the absorbent 

 function. 



To prove that the lacteals absorb chyle, it is only necessary to 

 examine them in a fasting and in a recently fed animal. In the 

 former their contents are transparent, in the latter they are milky, 

 and the opaque fluid can be shewn by simple means to move on in 

 the course indicated by the valves. That the lymphatics absorb 

 is perhaps best shewn by the phenomena of disease. The syphilitic 

 poison is frequently carried from the primary sore along the lym- 

 phatics, and exciting inflammation in this route may occasion 

 deposits of lymph or pus either on the penis or in the groin, and 

 the matter of abscesses so formed is capable of imparting the 

 disease to other individuals, thus proving the multiplication, and, 

 probably, also the real transport of the virus along these channels. 

 The inflammation of the lymphatic trunks and glands so often 

 observed to ensue upon accidental wounds, either poisoned or not, 

 especially in debilitated subjects, seems due to an actual propagation 

 * Paget's Report, 1844-5, p. 27. 



