28 FRANK ADAM McJUNKIN 
method used to demonstrate a non-lymphocytic group of mono- 
nuclear blood-cells is based on the ingestion by the cells of 
microscopic particles, a consideration of the phenomenon of 
phagocytosis so far as the ingestion of carbon is concerned 
becomes desirable. 
Although Langhans (’70) called attention to the ingestion of 
red-b'ood-corpuscles by the leucocytes in the tissues about 
hemorrhages, it was not until about 1883 that general attention 
was focused on the phagocytic activity of the cells of metazoa, 
at which time Metschnikoff (’83) began his publications on the 
subject. This activity of cells is often discussed in connection 
with such questions as immunity, the physiological atrophy of 
certain organs, removal from the tissues of mechanical irritants 
such as coal-dust, and the solution of dead cells and cellular 
debris. The ingestion of extraneous material is intimately 
related to the phenomena of chemotaxis ahd intracellular 
digestion. 
-Among the protozoa as among the differentiated cells of 
metazoa the ability to incorporate’ microscopic particles is 
present in some (amebae) and absent n others (trypanosomes). 
The determination of the phagocytic property of the cells present. 
in higher animals is less simple than it is of protozo6én cells, but 
experimentally microscopic particles may be brought into con- 
tact with many different living tissue cells. In distinction to 
true phagocytosis substances, such as bile pigment, hemoglobin, 
melanin, lead, and many other products, present normally or 
pathologically in the tissue may pass into the cells in solution 
and there be deposited as microscopic matter. The entrance in 
this manner of molecular and larger ultramicroscopic particles 
(colloids) into cells does not come under the term of phagocy- 
tosis which is a microscopic phenomenon of the cells. During 
phagocytosis the cytoplasm flows about the foreign body probabi. 
as the result of an alteration of surface tension (Wells, ’14) at 
the point of contact, while molecules and small colloids pass 
through the cell membrane by diffusion without any change in 
the cell contour, and it is likely that the two processes have a 
different explanation. The demonstration of microscopic foreign 
