MINOT : SINUSOIDAL CIKCULATION. 
211 
it seem to me that the essential intimate relation of the sinu¬ 
soid to an epithelial or epitheloid parenchyma is changed even if a 
minute layer of fibrillar tissue develops between them in the adult. 
Such a layer apparently occurs in the human liver, for instance, 
between the so-called “ capillaries ” and the liver-cells, according to 
observations made by Prof. F. B. Mallory with the aid of a new 
stain devised by him. 
3. Development. A capillary arises from a vasoformative cell, 
or chain of such cells, which becomes hollowed out and connected 
with other vessels at both ends ; it is therefore an addition by a 
new histogenesis to vessels previously differentiated. A sinusoid, 
on the contrary, is not the product of a new histogenesis; it does 
not arise directly from vasifactive cells, but results from the growth 
of the endothelial wall of a pre-existing blood vessel, and from the 
intercrescence of the growing endothelium with the developing 
parenchyma of the adjacent organ. It is possible that in some 
cases sinusoids arise by the expansion of capillaries — but such a pro¬ 
cess has not yet been observed. In regard to four organs Ave have 
direct observations as to the development of sinusoids, — namely, 
in the pronephros, the mesonephros, the liver, and the heart. For 
our present purpose we may regard the endocardium as an endo¬ 
thelial vein, and therefore say that in these four organs the sinu¬ 
soids are developed by the groicth a7id intercrescence on the one 
hand of the venous endothelium , and on the other of the paren¬ 
chyma (nepliric tubules, hepatic cylinders or muscles) of the 
organ. 
4. Endothelium. If the figures in this article are examined, it 
will be noticed that in every case the nuclei are much farther apart 
than one finds them in true capillaries. I have noted this pecul¬ 
iarity in all the sinusoids without exception which I have studied. 
This observation raises the question, is there a constant difference 
between the endothelium of sinusoids and of capillaries? This 
question cannot be answered at present. The recent observations 
however of Kupffer, ’99.1, compare also S. Mayer, ’99.1, show that the 
supposed endothelium of the sinusoids (capillaries) of the lobule of 
the adult mammalian liver is not a true endothelium, but a layer of 
more or less widely separated mesenchymal cells. Should subse¬ 
quent research prove that this peculiarity exists in other sinusoids, 
it would indicate an even greater morphological distinction between 
sinusoids and capillaries than now appears. 
