xiv THE LYMPH 509 



and dimensions, which are generally known as lymphatic spaces, 

 because they are full of lymph, may be observed. Again, the 

 tissues devoid of blood-vessels, like the cornea and the cartilages, 

 are provided with minute lacunar canaliculi, to which the 

 lymphatic humour necessary to cell nutrition penetrates. These 

 parenchymatous lymph spaces cannot be considered as lymph 

 capillaries, because they are not invested with the characteristic 

 epithelioid lining, which forms the true wall of the latter. They 

 represent a diffuse system of lacunae, interstitial to the cells 

 of the various tissues, which, according to Bichat's doctrine, is 

 generally regarded as the origin of the vascular lymphatic system, 

 i.e. of that provided with characteristic walls. In many inver- 

 tebrates the lacunar system, which has no proper wall, is the only 

 one that co-exists with the blood vascular system ; so that we may 

 logically regard the lymphatic vascular system as a perfecting, a 

 canalisation or successive centralising, of the primary lacunar or 

 interstitial system (Milne Edwards). 



We know that the lymph spaces communicate freely with the 

 lymph capillaries properly so-called, because a fluid stain such as 

 Prussian blue, when injected into the meshes of the subcutaneous 

 connective tissue by means of a syringe, penetrates to the interior 

 of the lymphatics, particularly if the oedematous swelling that 

 forms at the point of injection is compressed by the finger, so as 

 to increase the tension of the distended lacunar spaces and facilitate 

 the penetration of the coloured fluid -by the natural way of com- 

 munication with the lymphatics. 



(d) Besides the minute parenchymatous lymph spaces and 

 sinuses, the lymphatic capillaries and vessels communicate freely 

 with the serous cavity of the peritoneum, pleura, pericardium, 

 tunica vaginalis of the testicles, sub-arachnoid spaces, chambers of 

 the eye, membranous labyrinth of the ear, etc. So that these 

 larger and smaller cavities, which normally contain lymphatic 

 effusions, are, with regard to the system of lymphatic vessels, in the 

 same relation as the minute parenchymatous lymph spaces. The 

 researches of Kecklinghausen, of Ludwig and Schweigger-Seydel, 

 of Dogiel, of Eanvier and others, have shown this theory, as 

 previously enunciated by Mascagni, to be correct. It is easy with 

 Prussian blue to inject the lymphatic rete of the centre of the 

 diaphragm in a rabbit recently killed by bleeding and hung head 

 downwards, on pouring the stain into the abdominal cavity of the 

 diaphragm and assisting its penetration to the lymphatic rete of 

 the tendinous centre by means of artificial respiration with the 

 bellows (Fig. 243). On treating the excised diaphragm of a rabbit 

 with silver nitrate (1 in 300), the impregnation of the tendinous tissue 

 and epithelioid investment of the two faces, pleural and peritoneal, 

 reveals its structure and special disposition. On the pleural 

 surface the system of lymphatic vessels is shown in the form of 



