1C 4 MANUAL OF HISTOLOGY. 



found in one form or another wherever this tissue exists, and 

 constituting in the serous membranes a great absorbent sys- 

 tem, with its special connections, the lacteals, the lymphatic 

 nodes or glands, and the' fat-tracts. The important patho- 

 logical processes, both acute and chronic, connected with these 

 membranes are due principally to the fact that they are parts 

 of this great lymphatic system. 



Of course we must not lose sight of the connections of the 

 latter with the complimentary blood-vascular system ; the ten- 

 dency has been too much in the opposite direction, however, 

 and this more extensive, though less visible, system has been 

 too often neglected in favor of its more prominent companion, 

 in the consideration of processes of nutrition and of patho- 

 logical changes. 



General histology of the lymphatic system Previous 

 ideas. In describing the lymphatic system, only its general 

 histology will be considered, the details of its special distribu- 

 tion and arrangement being classed with the description of the 

 different organs with which it is associated. Since the serous 

 membranes have come to be regarded as important parts of the 

 lymphatic system, being, in fact, great membranous expansions 

 of that system, they are naturally and easily considered in con- 

 nection with each other. It is not intended to treat of them 

 here in their special details, but merely to make a general his- 

 tological study of them as a class. It is convenient to begin 

 with them in taking up the study of the origin of the lymphatic 

 system. 



With Virchow originated the theory that the starting-point 

 of the lymphatics is from hollow anastomosing cells, the con- 

 nective-tissue cells, whose prolongations communicate to form 

 continuous tubes. He termed them plasma cells. Kolliker 

 supported this doctrine, and a similar view was held by Ley- 

 dig. Henle held a different opinion, whilst Briicke and Ludwig 

 reverted to the ancient theory of Bichat, that the interstitial 

 spaces of the connective tissue are the true sources of the lym- 

 phatics. Recklinghausen, introducing nitrate of silver as a 

 reagent, showed that the lymphatic vessels are lined, and the 

 serous membranes covered, with flat cells, forming an endo- 

 thelial layer. He observed the passage of milk and fine gran- 

 ules, through openings in the central tendon of the diaphragm, 

 from the peritoneal to the pleural surface. He believed also 



