36 FRANK ADAM McJUNKIN 
B. EXPERIMENTS THAT SHOW THE ORIGIN OF THE PHAGOCYTIC 
MONONUCLEAR CELLS OF THE BLOOD FROM THE 
ENDOTHELIUM OF BLOOD VESSELS 
The points to be established by experiment are, first, the 
limitation of the phagocytosis of carbon to certain mononuclear 
cells of the blood and the endothelial cells lining the small blood- 
vessels and, second, absolute proof of the latter’s becoming free 
in the blood stream. There are other points discussed, such as 
a diminished power of immature neutrophiles (metamyelocytes) 
to ingest carbon, since they have a direct bearing on the question. 
a. Limitation of ingested carbon to the phagocytic mononuclear 
leucocytes of the blood and the endothelial cells 
of small blood-vessels 
The carbon (commercial lampblack ground for thirty minutes 
in a mortar) Was given intravenously to the animals (table 1) as 
a 5 per cent unfiltered suspension in | per cent gelatin. In both 
rabbits and dogs the suspension was injected into a vein of the 
left ear at the same time that the citrate was injected as a 10 
per cent solution into a vein of the right ear. The lampblack 
must not be thrown into the circulation too rapidly and the rate 
of the citrate injection must be controlled by the dyspnea that 
develops. Cover-glass films of blood were taken at varying 
intervals from the ear employed for the citrate injection and 
stained with polychrome blood stain. The films are made from 
drops of fresh blood of the exact size required. In the peripheral: 
blood of the rabbits (121, 138, 139, and 213) that received lamp- 
black alone very few carbon-containing mononuclear cells are 
present, although numerous polymorphonuclear leucocytes con- 
tain it. Thus in rabbit 139 one hour after the sixth injection 
less than 0.5 per cent carbon-containing mononuclear cells are 
present and on previous days none are found. In the blood of 
dog 151 four hours after the seventh injection of lampblack 
alone 2.15 per cent mononuclear carbon-containing cells along 
with 9.1 per cent carbon-containing polymorphonuclear leuco- 
cytes are present. Thirty minutes after the fifth injection there 
