THE LYMPHATIC SYSTEM. 169 



of silver, which produces so many doubtful pictures, may aid 

 in producing this appearance. The extreme mobility necessary 

 in some forms of connective tissue demauds extreme flexibility 

 as a quality of its elements, thus facilitating great variation in 

 structural arrangement under different conditions. 



Artificial injection of the lymphatics. If we inject this 

 tissue, by puncture with a hypodermic syringe, we can fill the 

 lymphatic vessels and 

 also the interstices, so 

 that they are continu- 

 ous ; but the question 

 whether this is a natur- 

 al or an artificial trans- 

 ition is one about which 

 histologists still differ. 

 Theoretically, we may 

 consider that such com- 

 munications exist to 



extent, at least FIG. 75. From mesentery of cat: silver-stained right por- 



. tion denuded of endothelium, showing, A. branched cells, with 



great] V increased B < intervening spaces ; left portion, endothelial layer preserved ; 



* C, pseucio-stornata ; D, nuclei ; E, elastic fibres. 



vascular tension takes 



place. But, at the same time, many, or even most of the in- 



terstices may be closed spaces. 



It is not a matter of great consequence, physiologically speak- 

 ing, since not only fluids but lymphoid corpuscles can penetrate 

 partitions which fail to resist so slight an injecting force as is 

 sufficient to unite these spaces and the lymphatic capillaries. 1 

 The fact that injections can be made without forming a com- 

 munication (Frey) does not prove that the latter does not 

 exist ; it may be due to an imperfect injection. As we shall 

 see later, the wandering propensities of the lymphoid cor- 

 puscles would almost exclude the possibility of the connective- 

 tissue interstices remaining closed spaces everywhere. 



Endothelium and stomata. We have already referred to 



1 Thoma and Arnold have shown that injections into the veins, in a living animal, 

 of insoluble coloring matters (not distending the vessels, however), pass between the 

 endothelial cells and find their way into the clefts and channels of the deeper tissues. 

 The possibility of absorption taking place through the intercellular substance which, 

 after all, may only be a semifluid material filling a space which varies in size under 

 different conditions, throws light on many of the difficult problems of absorption, 

 secretion, and excretion, and numerous pathological processes. 



