562 
ME. E. C. BABEE ON THE MINUTE ANATOMY 
the endothelial membrane are seen in figs. 5, c, & 6.) In these silver preparations a 
frequent appearance is that of a small artery traversing a lymphatic, and completely 
surrounded by a layer of endothelium, as represented in fig. 5, b. 
Once familiar with the appearances in preparations in which the silver injection has 
been successful, the walls of the lymphatic tubes and spaces may be recognized between 
almost all contiguous gland-vesicles in parts where the injection has not penetrated. 
They appear in this case as two fine dark wavy lines, studded at intervals with the 
nuclei of the endothelial cells seen in profile (figs. 13, 14, &c.). The nuclei then appear 
as staff-shaped bodies, and are of a much darker colour than when seen from their broad 
surface. The walls of the lymphatics presenting this appearance can usually be seen 
extending quite up to the free extremity of the inflexions mentioned above (p. 560). 
Where two vesicles are in apposition, it is not uncommon to see the two dark lines repre- 
senting the opposite endothelial walls separated for a short distance by a small quantity 
of a transparent material. 
It is possible that this appearance, attributed to the lymphatics, may in some instances 
be produced by capillary blood-vessels. Judging, however, from specimens in which 
the lymphatics are injected, it is probable that we have to do with such vessels, although 
it is not possible to distinguish the nucleated membrane forming the wall of a capillary 
blood-vessel from that of a lymphatic. 
The Contents of the Lymphatics. — Before concluding this description of the lym- 
phatics I must say a few words with regard to the contents of these vessels. 
On examining the lymphatic vessels in a specimen injected with Berlin blue, and 
stained with picrocarminate of ammonia, by far the greater part of their cavity is seen 
to be filled with a granular material of a more or less bright yellow colour. The blue 
injection occupies the peripheral portion of the lumen of the vessel, forming bands of 
colouring-matter between the wall of the vessel and its contents. In fig. 1, b represents 
the granular contents of a lymphatic vessel, and the dark line surrounding this indicates 
the position of the injection. On examining the lymphatic tubes some of them are seen 
to contain this granular material ; the greater part, however, in a well-injected specimen, 
are filled with blue injection. It is probable that the injection first entering the smaller 
tubes, i. e. the rootlets, forces their contents, or at least a part of them, onwards into the 
larger tubes, and from these into the lymphatic vessels. From the relation existing 
between the injection and the contents of the vessels, I am led to the belief that during 
life the contents are of a viscid consistence. This conclusion results from the following 
considerations : — If at the time of the injection the contents were fluid, or of the con- 
sistence of ordinary lymph, the injection on entering the vessels would either force the 
contents of the same before it or commingle with them. The injection, however, was 
performed immediately after death, before the contents could have had time to coagulate ; 
and the injection, as we have seen, does not mix with the contents, but forms a separate 
layer between them and the wall of the vessel. It therefore follows that the contents 
of the lymphatic vessels must during life have been more or less viscid in character. 
