38 FRANK ADAM McJUNKIN 
injection there are 0.49 per cent carbon-containing mononuclear 
leucocytes and 3.21 per cent polymorphonuclear ones. In rabbit 
208 there are present five hours after injection 6.9 per cent 
polymorphonuclear leucocytes with carbon, but no carbon-con- 
taining mononuclear cells. In the blood of dog 209 no earbon- 
containing cells are present twenty-four hours after injection. 
Again in rabbit 212 no cells with carbon are present after 
twenty-four hours. 
The intravascular phagocytosis of carbon is readily produced. 
After large injection of non-citrated carbon suspensions repeated 
a number of times, as many as 2.15 per cent of the mononuclear 
cells (dog) may contain carbon, and after single injections of 
smaller amounts of carbon together with large doses of citrate 
3.03 per cent mononuclear leucocytes may contain carbon two 
hours after injection with the reduction of carbon-containing 
polymorphonuclear ones to a minimum (less than 1 per cent). 
The number of phagocytic cells in the peripheral blood varies in 
different animals, reaching a maximum in one-half to two hours 
with a very noticeable diminution in five hours and a total 
disappearance of cells with carbon within twenty-four hours. 
The disappearance within twenty-four hours from the periph- 
eral circulation of all cells that have incorporated foreign 
particles appears.to explain perfectly the failure of Evans (15) 
and others to find vitally stained cells in the peripheral blood, 
since the cells stained by the intra vitam methods contain 
microscopic particles and considerable time (more than twenty- 
four hours) and frequently multiple injections of the dye are 
required. 
The limitation of the ingested carbon to the. mononuclear . 
cells of the blood (3 per cent in some animals) and to endothelial 
cells lining the capillaries of various organs is of the nature of 
a highly specific stain. In dog 209 (fig. 6) two or three and 
less commonly more perfectly round carbon-containing mono- 
nuclear cells may be found in the sinusoids of the liver which are 
lined with elongated carbon-containing endothelial cells. The 
» round contour of the former and an elongation due to ameboid 
motion (fig. 5) is a differential point between the two. There 
