44 FRANK ADAM McJUNKIN 
closed channels lined with endothelial cells which have nothing 
in common with the lymphoblastic cells. In the lymph nodes, 
therefore, there are present two varieties of endothelial cells 
(those lining blood-vessels and those lining lymph-sinuses) and 
the lymphoblastic cells. Twenty-four hours after a single intra- 
venous injection (dog 176) the endothelial cells lining the capil- 
laries are the only cells that contain carbon. Even in the 
germinal centers made up of large proliferating lymphoblasts 
carbon is present in the endothelial cells of the capillaries 
(fig. 11). Later (dog 151) carbon-containing cells migrate into 
the lymphoblastic tissue, and then there is an admixture of 
carbon-containing cells and lymphoblasts. This origin of phago- 
cytic cells from blood-vessels in the germinal centers has been 
lost sight of by some. 
TABLE 2 
el HOURS KILLED 
NO. ANIMAL oe eae, DOSE OF CARBON AFTER 
r more LAST INJECTION 
130 Rabbit 6 da. 5 ec. four times 24 hours 
152 Dog 10 da. 10 cc. five times * 24 hours 
177 Dog 1 da. 40 ce. once 24 hours 
210 Dog 1 da. 30 ce. once 24 hours 
211 Guinea-pig 30 min. 5 ec. once 30 min. 
212 Guinea-pig 2 hrs. 5 ec. once 2 hours 
In (dog 151) a deeply pigmented node was found in the retro- 
peritoneal tissue below the liver. The structure of this gland 
strongly suggests a hemolymph gland. With this exception, no 
markedly blackened nodes have been found in animals receiving 
intravenous injections. 
In one etherized animal (dog 152) lymph was obtained from 
the thoracic duct and no cells (count of 500) containing carbon 
are present. Owing to irregularities in the course of the lymph- 
vessels, some difficulty has been encountered in freeing the 
vessels near their entrance into the jugular or subclavian, but 
once dissected free collection of the lymph is easy. Coagu- 
lation is prevented by 5 mg. citrate per cubic centimeter and the 
fluid centrifuged. Smears from the sediment are fixed in 
alecohol-ether to free them from fat and stained in the usual way. 
