30 ANATOMY OF THE LYMPHATIC SYSTEM. 



appears under the endothelium of the general surface a second layer 

 of large flat cells, arranged very similarly to an endothelium. The 

 cells consist of an almost hyaline substance, and possess a large clear 

 ovoid nucleus : the cells which lie deeper in the proper substance of 

 the serosa are more or less flat and branched. In preparations which 

 have been stained with nitrate of silver after being pencilled from the 

 pleural surface, the branched cells of the serosa are not easily recog- 

 nisable, the lymph-canalicular system of the branched cells being the 

 chief thing that comes into view ; but by using a high power and 

 examining a preparation which has been deeply stained in many 

 places, one is able to distinguish the bodies as well as the processes of 

 the branched cells, the former occupying the lacunae, the latter the 

 canaliculi of the lymph-canalicular system. The cell substance is 

 very pale, distinctly granular round the oblong or spherical sharp 

 outlined nucleus. 



The cells of the islands of the serosa, which are surrounded by 

 lymphatic vessels (see the following chapter), are very instructive as 

 regards the processes of division of the branched cells of the lymph- 

 canalicular system we have already mentioned in a former place. One 

 finds in the central parts, as well as in the peripheral parts of those 

 islands, numerous places where the branched celkjie in groups, as if 

 round a common centre or in chains : there the individual cells are 

 very little or not at all branched where they touch each other, whereas 

 they are provided with processes on their outer sides. These cells of 

 the serosa come out very distinctly when the serosa has been slightly 

 affected by inflammation. Under those circumstances their relation 

 towards each other and the surrounding parts is much more distinct. 

 We call the attention of the reader to the figures 14, 16, 17, which 

 will render our meaning easier to understand than any long descrip- 

 tion. 



