322 The Circulation through the Dog’s Spleen 
Numerous experiments upon the dog’s spleen show conclusively that 
the walls of the venous plexus are very porous. This can be shown well 
by injecting aqueous Prussian blue into the vein, which ‘gradually 
passes through its walls at every point. If granules a little larger are 
injected (cinnabar), it will be found that they also pass through easily, 
but still larger granules (ultramarine blue) pass through the walls of 
the veins with greater difficulty. Yet often many of these granules 
pass through the vein-wall at all points, showing that it is very porous. 
Around the Malpighian follicles there is always an extensive “ extrava- 
sation,’ showing that the openings at this point are very large and 
numerous. So constant is this “extravasation” found that it is out 
of the question to consider the openings around the follicles as artificial. 
The nature of the wall of the vein has been well demonstrated by 
Hohl,” who gives an excellent picture of it (Fig. 10). It is composed 
of an extremely dense network of fibrils which withstand the action of 
pancreatin, and is therefore not elastic in nature. Hohl considers 
the fibrils as belonging to the reticular group, for they anastomose fre- 
quently and are directly continuous with the reticulum of the pulp. 
The fibrils around the vein were first isolated by Henle by means of 
a diluted solution of potassium hydrate, and for this reason v. Ebner ~ 
considers them as elastic tissue, a conclusion which he supports with the 
Unna-Tiinzer stain for elastic tissue. It is well known that reticulum 
fibrils as well as white fibrous tissue fibrils do become transparent in 
diluted solutions of potassium hydrate, but that their sharpness is again 
brought out in case they are stretched,” a condition easily obtained 
under the cover-glass by slight pressure upon it. Von Schumacher” 
repeated y. Ebner’s tests for elastic tissue in the veins of the dog’s 
spleen and sometimes found numerous elastic fibrils encircling them 
and at other times none at all. These tests have been repeated by 
Hohl” and by Hoyer,” who find that all or nearly all of the fibrils are 
reticular, which may be accompanied by some elastic fibers. In tests 
made with Weigert’s elastic tissue stain I have been unable to find any 
elastic fibrils accompanying the reticulum fibers encircling the smaller 
veins. It is well when staining for elastic tissue not to stain too long, 
12 Hohl, Archiv fiir Anatomie, 1897. 
3 Henle, Anatomie, IT, 1866. 
14 Von Ebner, Anat. Anz., XV, 1899. 
15 Mall, Abhandl. d. k. sich. Gesellsch. d. Wiss., XIV, 1890. 
16 Von Schumacher, Arch. f. mik. Anat., LV, 1899. 
17 Hohl, Anat. Anz., XVII, 1900. 
18 Hoyer, Anat. Anz., XVII, 1900. 
