16 Papers from the Department of Marine Biology. 
and discharge of granular material, are familiar steps in the process of 
secretion. This activity is undoubtedly aided greatly by the large, 
irregular nucleus. It is evident that a lobular, branching nucleus has 
a much greater surface-area than a spherical nucleus of equal volume. 
Interaction of nuclear and cytoplasmic materials is thus facilitated. 
Irregular branching nuclei, moreover, are known to occur in gland-cells, 
for example, in the spinning glands of the caterpillar. These cells in 
the skates are also in very close relation to the blood-stream. Wax 
reconstructions of the capillaries near some of the cells have been made, 
which show that one of the cells is usually touched by four or five 
capillaries (fig. 2). Indeed, I have found several cases in which a cap- 
illary for a part of its course was entirely surrounded by the cytoplasm 
of one of the cells. Such an intimate relation of the cells to the blood- 
vessels makes it favorable for them to extract from the blood the raw 
materials that they require for their activities and also for them to give 
back their specific secretion. Furthermore, the lack of a definite cell 
membrane, and the consequent loose integration of the cell cytoplasm, 
is favorable to glandular activity. 
PHAGOCYTE HYPOTHESIS AND VITAL STAINING EXPERIMENTS. 
E. V. Cowdry called the attention of the writer to the morphological 
resemblance of these cells of the skate spinal cord to the giant cells of the 
miliary tubercle. He suggested that instead of their being gland-cells 
they might in reality be phagocytes; that the granules instead of being 
secreted were being ingested. This hypothesis has some evidence in its 
favor and deserves careful consideration. 
The giant tubercle cells have been shown to be pure colonies of 
endothelial macrophages. The term “‘macrophage”’ has been used by 
Evans to designate a certain class of cell which reacts in a definite way 
toward fine particles. He finds that when trypan blue, or certain other 
dyes of the benzidine series, is injected into living animals, the dye is 
taken up by certain groups of cells, the macrophages. These macro- 
phages are abundantly present throughout the body, and line the blood- 
current itself in the liver, bone marrow, and spleen. Endothelium in 
most parts of the body may become phagocytic. Even in the central 
nervous system, which is usually unaffected even in animals whose 
tissues take an intense vital stain, the glial cells have been found to 
awaken in the case of lesions and to transform themselves into macro- 
phages; and the endothelium of neural vessels may be similarly affected. 
The macrophages handle fats and fat-like bodies and the blood and 
bile pigments. Evans states: 
“We may define macrophages as mononuclear cells wherever they may 
be, lining vascular channels, resident in connective tissue, or entirely free, 
whose protoplasm constitutes a physical system characterized above all by its 
response to finely particulate matter. In case of particles of ordinary micro- 
