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The Circulation through the Dog’s Spleen 
submaxillary gland of the pig and found that they arise from a syn- 
eytium and are fibrillar (pp. 5 and 10), even if in transverse sections 
they appear homogeneous. If we could add to such preparations an 
excessive stain for elastic tissue it is easy to conclude, as v. Ebner did, 
that these basement membranes are also homogeneous and elastic. 
Since, however, the elastic membranes are not present in the veins of 
the dog’s spleen they do not stand in the way of an open circulation in 
this animal. 
Recently Weidenreich has asserted that there are numerous lymphatics 
in the spleen which empty directly into the veins of this organ. This 
is only another way of expressing what W. Miiller stated a number of 
years ago. It is easy to state that the channels from the pulp to the 
veins are lymphatics, but in view of the work of Ranvier,” MacCallum ™ 
and Sabin” our conception of lymphatics has been greatly sharpened. 
According to Sabin all of the lymphatic channels arise from four 
points from the veins, which correspond with the lymph hearts, and 
then spread all over the whole body. In order to accept Muller’s notion 
it must be shown that lymphatics have an independent origin the spleen, 
which is very improbable. 
Judging by the structure of the vascular system of the spleen-pulp, 
it is not remarkable that numerous investigators have concluded that 
the circulation should be directly through the pulp-spaces. That this 
should be so appears very remarkable when the circulation through other 
organs and tissues is considered, where the capillary walls are lined by 
a complete layer of endothelial cells and their lumina are equal. No 
one admits, however, that such capillaries are within the spleen pulp, 
but because they are closed elsewhere it is concluded that they must also 
be closed within the spleen. If the ease with which * extravasations ” 
take place from the capillaries of embryos, when the blood-ves- 
sels are injected, is recalled, one is struck with the similagity 
between them and those of the spleen-pulp. In fact I have fre- 
quently observed that in certain portions of the embryo the * extrava- 
“sation” takes place with greater constancy than elsewhere. Recently 
this system of irregular capillaries has been more sharply defined by 
Minot,” who terms them sinusoids and shows that a sinusoidal circula- 
tion is present in many of the organs of the embryo and in some of the 
organs of the adult. He states that he does not consider it improbable 
that the circulation through the spleen will prove to be sinusoidal. That 
2> Ranvier, Archiv d’ Anatomie, I, 1897. 
26 MacCallum, Archiv fiir Anatomie, 1902. 
“Sabin, Amer. Jour. Anat., I, 1902. 
28 Minot, Proc. Bost. Soc. of Nat. History, X XIX, 1900. 
