THE RED PARTICLES. 281 



SECT. 95. In chapter II we considered the lymphatic vessels 

 arising from the cells of the spleen as its excretory ducts, which 

 term, perhaps, when applied to lymphatic vessels, may be ob- 

 jected to by some, but we think not with reason; for if we 

 consider the office of an excretory duct, we shall find that there 

 is no more impropriety in calling these lymphatics excretory 

 ducts, than there is in using the term excretory duct to ex- 

 press that tube which conveys the secreted fluid of any other 

 gland to its place of destination. The excretory duct of the 

 liver conveys the bile into the duodenum, because that fluid is 

 required in the intestines for the purpose of digestion. So the 



elementary molecules in a liquid cytoblastema, both produced by the 

 old cells. This liquid and the molecules might traverse the exquisitely 

 delicate membrane described by Mr. Simon, get into the lymphatic 

 vessels, and keep up the supply of globules there ; and it is not im- 

 possible that part of the membrane itself, as well as the highly developed 

 epithelium* of the intra-glandular lymphatic vessels, and the lymph- 

 globules themselves may be constantly in a state of dissolution and re- 

 novation. 



But leaving these hypotheses, we come to the fact that the lymphatic 

 vessels of the thymus do carry a fluid, however it may get into them, 

 like that of the thymus, and pervaded by the same globules. At least 

 such is the result of Hewson's observations, which, as far as I know, 

 have never been refuted on this point ; and Sir Astley Cooper, whose 

 view of the use of the gland is mentioned in Note CXXVTI, p. 261, de- 

 clares that its lymphatic vessels are its absorbent ducts, and the carriers 

 of its fluid into the veins in the lower part of the neck. I must repeat 

 that a careful inquiry into the nature of the contents of these absorbent 

 vessels ought, as Hew son and Cooper believed, to form a leading part 

 of any researches concerning the office of the thymus. 



In the Appendix to the English edition of Gerber's 'Anatomy,' 

 pp. 95-100, the reasons are detailed which induce me to believe, that 

 the fluid of the thymus differs only from that of the lymphatic glands 

 in containing more corpuscles ; that these have the characters of nuclei 

 or immature cells ; b and that both the lymphatic glands and the thymus 

 are organs for the elaboration of nutritive matter, the activity of the 

 thymus being most remarkable at that period of the economy when 

 growth and nutrition are most active: see Note cxxvn, p. 261. 

 Whether the ultimate destination of these embryo cells be simply to 

 serve as central particles for the formation of blood-corpuscles, as 

 Hewson supposed, or for the foundations, either mediately or imme- 

 diately, of cells concerned in growth and nutrition generally, as the 

 recent cell-doctrine would imply, is another question deserving of 

 further inquiry. 



* See Note cxix*, p. 250. b See Note cxxn, pp. 223-4. 



