Chap, xiv.] LYMPHATIC CIRCULATION. 225 



they are more numerous in the mammifers, and largely aided 

 in their cellular production by organs of analogous structure, 

 varying iu size from that of a lentil to that of a nut, and dis- 

 seminated along the passage of the lymphatic vessels ; they are 

 lymphatic ganglions, which are met with already in birds, in the 

 region of the neck. The lymphatic vessels are subdivided into 

 fine afferent canalicules before approaching a ganglion, and on 

 the other side of the gland the vessel only foims again at the 

 expense of analogous efferent canalicules. As to the ganglions 

 they are like the Peyer's glands, essentially constituted by 

 vesicles, at least the tenth of a millim^re large, and filled with 

 nucleated cells, with a diameter of about five-thousandths of a 

 millimetre. By the rupture of the vesicles the cells become free 

 and are borne along by the lymphatic plasma. 



As we have seen, the lymph is a living liquid, playing in 

 nutrition an important part ; thus it is that the ligature of the 

 thoracic canal causes the i-apid emaciation of the mammifers, and 

 their death at the end of a small number of days. 



Trusting to the preceding data, we can form conjectures suf- 

 ficiently probable respecting the physiological province of the 

 lymphatic system. The lymph has in the vertebrated organism 

 a double origin. A notable fraction of the substances which 

 constitute it is drawn from the intestinal mucous membrane. 

 It is principally in this way that the fat, emulsionised bodies 

 penetrate into the circulation. But the networks, lymphatic in 

 origin, of the rest of the body, appear to gather a part of the 

 plasma completely elaborated, which pierces by osmosis through 

 the wall of the vessels, and especially of the fine arteries and 

 capillaries. To this sanguineous plasma comes probably to join 

 itself a part of the intercellular blastema, that is to say, of 

 the assimilable liquid which bathes the anatomical elements 

 apai-t from the vessels. The whole forms, first of all, a sort of 

 blood destitute of globules, a limpid plasma ; but at the expense 

 of this plasma white globules form ia the ganglions. Then the 

 lymph is complete, and it has the greatest analogy of chemical 



Q 



