310 



ABSOEPTIOK 



have indicated the probable existence of stomata, of variable size and irregular shape, in 

 the smallest vessels ; but it must be acknowledged that one of the strongest arguments 

 in favor of the existence of these orifices is, not their anatomical demonstration, but the 

 fact of the actual passage, through the walls of the vessels, of fatty particles, the en- 

 trance of which cannot be explained by the well-known laws of endosmosis. The ana- 



FIG. 91. Lymphatic plexus, showing the epithelial lining of the vessels. (Belaieff.) 



tomical evidence of the existence of openings is derived mainly from preparations stained 

 with nitrate of silver. It is assumed that nitrate of silver stains the solid parts of tis- 

 sues and the borders of the epithelial cells, and that areas which do not present any 

 staining are necessarily open, If this be true, and this view is now very generally ac- 

 cepted, we may consider the existence of openings in the lymphatic vessels as demon- 

 strated. In preparations of the lymphatics, the solution of silver is seen staining the 

 tissues and the borders of the epithelial cells lining the vessels ; but there are areas be- 

 tween these cells where no staining is observed and in which no nuclei are brought on 

 by staining with carmine. It is not impossible, however, that the solutions used may 

 fail to attack all parts of the tissue, and that these colorless areas may be closed by an 

 amorphous membrane. 



With regard to the origin of the lymphatics in the tissues, it does not seem that our 

 actual knowledge extends beyond the small vessels, such as are observed in the superfi- 

 cial net-work of the skin. Within the last few years, Kecklinghausen and others have 

 assumed the existence, in the connective tissue (which is so widely distributed in the 

 organism), of minute tubes or canaliculi, which open into the lymphatic vessels, and that 

 these are the true vessels of origin of a great part of the lymphatic system. These lit- 

 tle vessels are called serous canaliculi. This view, however, is not sustained by positive 

 demonstration and must be regarded as purely hypothetical ; and the same may be said 

 of the opinion advanced by some that the lymphatics originate in lacunae or spaces in the 

 connective tissue or in a system of canals formed by connective-tissue corpuscles and 

 fibres. Sappey asserts very emphatically that not one lymphatic vessel has ever been 

 demonstrated as arising from the substance of connective tissue ; and a careful study of 

 recent observations in Germany shows this to be the fact. 



Lymphatic Glands. In the course of the lymphatic vessels, are found numerous small, 



