LYMPHATIC GLANDS. 283 



in the small intestine of a mouse, Poiseuille saw the chyle 

 moving with intermittent propulsions that appeared to corre- 

 spond with the peristaltic movements of the intestine. But for 

 the general propulsion of the lymph and chyle, it is probable 

 that, together with the vis a tergo resulting from absorption 

 (as 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 proba- 

 bly 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 removal of his leg by am- 

 putation, 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 undulatory movements, but in a uniform con- 

 traction 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 lym- 

 phatic glands (Fig. 99). 



A lymphatic gland is covered externally by a capsule of 

 connective tissue, which invests and supports the glandular 

 structure within ; while prolonged from its inner surface are 

 processes QYtrabeculw which, entering the gland from all sides, 

 and freely communicating, form a fibrous scaffolding or strorna 

 in all parts of the interior. Thus are formed in the outer or 

 cortical part of the glands (Fig. 96), in the intervals of the 

 trabeculse, certain intercommunicating spaces termed alveoli; 

 while a finer meshwork is formed in the more central or 

 medullary part. In the alveoli and the trabecular meshwork 

 the proper gland-substance is contained ; in the form of nod- 



