260 GENERAL ANATOMY. 



passages, more extended and more multiplied, than those of 

 the known blood vessels. 



J. Blenland* has added to these reasons an anatomical ex- 

 periment, which, if it were repeated and confirmed, would 

 furnish the most powerful argument in favour of the existence 

 of serous vessels. 



It is known that the red injection, which is fine and very 

 penetrating, easily passes from the arteries into the veins 

 through the intermediate capillary vessels. It is equally known, 

 that colouring matter remains in the capillaries, even whilst its 

 vehicle transudes and is infiltrated in the surrounding sub- 

 stance, where, from the want of colour, it is impossible to dis- 

 cern any form or any particular direction in the passages or 

 reservoirs into which the injection has made its escape. Blen- 

 land formed the idea of combining with the red colouring mat- 

 ter another white matter, which instead of being pulverulent 

 and suspended in the vehicle, was dissolved in it. Having 

 pushed his injection into the arteries of a part of the intestine, 

 of which the vessels were previously filled with a coarser mat- 

 ter and of another colour, and having afterwards separated the 

 peritoneal coat from the intestine, he observed in the external 

 surface of that membrane, by the aid of the microscope, be- 

 sides the capillary blood-vessels, which were all filled with red 

 matter, another order of finer and white vessels, arising from 

 the smallest arteries which had admitted the red injection, and 

 entirely different from the vessels which are filled by ordinary 

 injection. 



But what are these white microscopical vascula or very minute 

 vessels, seen but once, and on a portion of membrane detached 

 from the neighbouring parts? Are they exhalent arterioles, 

 opening at the surface of the peritoneum? Are they serous ar- 

 terioles continuous with serous radicles of veins, and consti- 

 tuting a serous capillary system? Finally, are they lymphatic 

 arterioles, continuous with radicles of lymphatic vessels? It is 



* Experimentum anatomicum, quo arieriohrum lymphaticarum existentia 

 probabilitcr adstruitur, instituturn, descriptum, ct icone illustratum. Lugd. 

 Bat. 1784, 4to. 



