ORIGIN OF PHAGOCYTIC MONONUCLEAR CELLS Al 
parenchymal cells are normal, cells resulting from mitoses neces- 
sarily enter the blood stream since the capillaries cannot lengthen. 
It is true that the dividing endothelial cells in the lengthening of 
vessels in granulation tissue often remain more or less elongated 
during division, but the demonstration of mitroses in vessels 
that are not lengthening is more certain proof of the entrance of 
these cells into the blood stream. A careful search in the liver 
of animals one to three days after a lampblack-citrate-typhoid 
injection shows the presence of mitoses in endothelial cells with 
particles of lampblack in them (figs. 1 and 2). In an organ such 
as the heart (fig. 3) in which the capillary wall is somewhat 
thicker than that of the sinusoids of the liver the relationship 
of the dividing cell is better defined. 
c. The phagocytic activity of immature myeloblastic cells 
The identification of cells in sections of bone-marrow stained 
with eosin-methylene blue is less certain than in smears, 
although the position of the cells in the tissue is helpful. The 
relationship of bone-marrow structures is difficult to determine 
and the exact location of the myeloblastic-cells as regards the 
endothelial lin‘ng of vessels is not easy to make out even in the 
best paraffin sections. In the animals receiving single doses of 
both lampblack and citrate examination of sections of bone- 
marrow shows little if any carbon in any cells except the endo- 
thelial cells lining the blood-vessels and an occasional mono- 
nuclear phagocyte in the lumen of the vessels. The only other 
cells in which carbon may be found are small numbers of mature 
polymorphonuclear leucocytes. The younger myeloblastic cells 
(myelocytes and metamyelocytes) contain little carbon. On the 
other hand in animals that have received lampblack alone the 
carbon is present not only in the endothelial cells of the vessels, 
but also in many of the polymorphonuclear leucocytes. In 
these animals myelocytes are almost free of carbon. In the 
cells that have become older and smaller with shrinkage of the 
nucleus (so-called metamyelocyte) there is an occasional one 
that has ingested the carbon. 
In smears properly prepared the cells have the appearance 
