35 8 ABSORPTION. 



resulting from absorption (as shown in the ascent of sap in 

 a tree), and from external pressure, some of the force may 

 be derived from the contractility of the vessel's own walls. 

 Kolliker, after watching the lymphatics in the transparent 

 tail of the tadpole, states that no distinct movements of 

 their walls can ever be seen, but as they are emptied after 

 death they gradually contract, and then, after some time, 

 again dilate to their former size, exactly as the small 

 arteries do under the like circumstances. Thus, also, the 

 larger vessels in the human subject commonly empty 

 themselves after death ; so that, although absorption is 

 probably usually going on just before the time of death, it 

 is not common to see the lymphatic or lacteal vessels full. 

 Their power of contraction under the influence of stimuli 

 has been demonstrated by Kolliker, who applied the wire 

 of an electro-magnetic apparatus to some well-filled 

 lymphatics on the skin of a boy's foot, just after the re- 

 moval of his leg by amputation, and noticed that the 

 calibre of the vessels diminished at least one half. It is 

 most probable that this contraction of the vessels occurs 

 during life, and that it consists, not in peristaltic or undu- 

 latory movements, but in an uniform contraction of the 

 successive portions of the vessels, by which pressure is 

 steadily exercised upon their contents, and which alternates 

 with their relaxation. 



Lymphatic Glands. 



Almost all lymphatic and lacteal vessels in some part of 

 their course pass through one or more small bodies called 

 lymphatic glands (fig. 94). These are something more 

 than mere plexuses of the vessels. 



Each gland has an investing capsule of connective tissue, 

 from which prolongations dip into its substance forming 

 partitions. Immediately within the investing capsule 

 occurs what is named the cortical portion of the gland 

 'fig. 94, c\ and immediately within this the medullary 



