40 FRANK ADAM McJUNKIN 
b. Mitosis of carbon-containing cells in the walls of blood 
vessels that are not lengthening 
The identical behavior to carbon of the phagocytic mono- 
nuclear leucocytes of the blood and the phagocytic endothelial 
cells of the capillaries is evident and observations to show that 
most normal extravascular tissue contains practically no phago- 
cytic cells may be readily made. That mononuclear phagocytes 
of the blood arise from the endothelial cells lining the capillaries 
may be demonstrated by a careful histologic technic. A desqua- 
mation into the lumen of a vessel is frequently spoken of, but 
there seems to be little evidence of such a process aside from the 
formation of a new cell by mitosis. In routine autopsy exami- 
nations an occasional mitotic figure may be found after prolonged 
search in the endothelial cells of capillaries in the liver, pancreas, 
and other organs. In the animals that received no typhoid 
bacilli, such as rabbit 188 (fig. 3), prolonged search is required 
to find a karyokinetic figure, and even the accumulation of 
enormous amounts of carbon in the cells (dog 151) does not 
increase the proliferation of the endothelial cells to any ap- 
preciable extent. In animals receiving typhoid bacilli (dog 209) 
mitoses (figs. 1, 2, and 4) may be demonstrated with much 
greater ease. A careful histologic technic is required and demon- 
stration of the achromatic spindle is necessary for certain in- 
dentification, since the dense polymorphous nuclei of neutro- 
philes, pyknotie nuclei of endothelial cells and even masses of 
carbon may be confused with imperfect division figures, and 
judging from the comparatively small number of the mitoses in 
many of the animals receiving intravenous injections, such 
mistakes have not been uncommon. ‘The tissues were removed 
from the body immediately after the animal was killed and 
pieces 2 mm. thick placed in Zenker’s fluid. After embedding in 
paraffin, sections not more than 7 » thick were cut and stained 
by the eosin-methylene blue method of Mallory. 
The endothelial cells of the liver contain more carbon than 
those of other organs and is well adapted for a search for mitoses. 
In the liver, heart, kidney, and other solid organs in which the 
