318 The Cireulation through the Dog’s Spleen 
Thoma and Weidenreich, they have had in reality the same kind of 
specimens before them. Weidenreich’s single complete capillary, which 
is extremely difficult to obtain when the spleen is not injected, is 
Thoma’s Zwischenstiick, quite easily found when hyperaemic spleens 
are injected with fine granular masses. On the other hand Thoma’s 
extravasations, which are always present, represent the normal course 
according to \Weidenreich. So it seems to me that all of the recent 
workers practically agree regarding the walls of the capillary vessels of 
the spleen, and the question formulates itself anew, How complete is 
the capillary wall, and is it exactly the same in all portions of the spleen? 
With this there is joined a second but most important question, Do all 
of the blood corpuscles enter the pulp-space in passing from the artery to 
the vein? Both of these questions must be answered by making experi- 
ments and injections. To attempt them through simple sections of the 
spleen, no matter how thin they may be, is practically a waste of time. 
For purposes of description I have shown that it is well to divide the 
spleen into a number of lobules,’ which are practically identical in 
arrangement with those of the liver. Each lobule is about a millimeter 
in diameter with its artery in the centre and its main veins and trabeculae 
on the periphery. There are about 80,000 lobules in the dog’s spleen. 
Each lobule is broken up into terminal or histological units, one for 
each terminal artery or ampulla. Around this there is some spleen 
pulp which lies within one of the meshes of the venous plexus. This is 
well shown. in Fig. 13 in my paper in the Zeitschrift fiir Morphologie 
und Anthropologie. The arteries of the lobule are covered with a 
lymphatic sheath continued from the Malpighian follicle, known as the 
ellipsoid sheath. This ellipsoid of Schweigger-Seidel* continues to the 
end of the artery as a small group of round cells (see figure) and marks 
the beginning of the ampulla. Assuming then that the ampulla com- 
municates with the venous plexus, it may be divided into three parts. 
The first third, which is the ampulla proper of Thoma; the second third, 
which contains large side openings, and the third third, which is 
Thoma’s Zwischenstiick. For the present I shall speak of the ampulla 
in this way, even if at times it appears to contain neither cavity nor 
walls. The capillary veins or venous plexus flow together into intra- 
lobular collecting veins, which in turn empty into the interlobular veins 
lying within the trabeculae at the periphery of the lobule. 
The division of the spleen into lobes and lobules is not new. Kyber ° 
®§Mall, Zeit. f. Morphologie u. Anthropologie, 1900. 
™Schweigger-Seidel, Virch. Arch., XXIII. 
8 Kyber, Arch. f. mik. Anat., Bd. VI, 547. 
