THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 49 



puscles is going on from the endothelium of the lymphatics directly 

 into the lumen of this latter. 



(d.) Relation of the Lymphatic Vessels to the Surface of the 

 Serous Membranes. 



It is held by many histologists that there exist in many 

 serous membranes discontinuities between the endothelium of the 

 surface, by which discontinuities stomata a superficial lymphatic 

 vessel may communicate with the free surface. That there must 

 exist stomata on the abdominal surface of the centrum tendineum 

 has been proved by the well-known experiments of Reckling- 

 hausen. After Recklinghausen, several observers have shown the 

 absorption of dissolved and undissolved substances, injected into 

 the serous cavity, from the lymphatics of the serous membrane. 

 There have been also several observers who tried to show on silver- 

 stained preparations those stomata. They have, namely, shown that 

 there exist small circular or angular dark or light fields between the 

 common large polygonal endothelial cells. These small fields were either 

 single or in small groups not very far apart from each other ; they 

 were of different size, and where they appeared to be regularly dis- 

 tributed they were found to represent the centre of a larger or smaller 

 group of endothelial cells, radiating towards that centre. 



That in many serous membranes stained with nitrate of silver such 

 figures occur there can be no doubt whatever, but it is a quite dif- 

 ferent question whether they correspond really to holes. For, on the 

 one hand, it can be shown that these figures are sometimes to be found 

 on places, and not very rarely, where there are no lymphatic vessels 

 just below that part, e.g. on the centrum tendineum : on the other 

 hand, in the same preparation, they are not to be found where 

 they ought to be, namely, below where a superficial lymphatic vessel 

 lies. Besides, from their irregular distribution, their irregular shape 

 and size, one would be more inclined to take them as accidental than 

 as anatomical structures. 



The histological proof that lymphatic vessels stand freely in 

 communication with the surface has been brought forward until now, 



E 



