30 FRANK ADAM McJUNKIN 
this cell. In this particular case it has been stated by some that 
only the younger cells manifest such activities, yet here the 
characteristic fibrils must be present, for they appear in this cell 
within twenty-four to forty-eight hours after mitosis, in which 
time’ ingested particles could scarcely be disposed of. Ingested 
foreign particles, such as carbon, or other cells, such as red 
blood corpuscles, neutrophiles, or lymphocytes, have not been 
demonstrated in fibroblasts stained in such a way as to bring 
out the characteristic fibrils either in human or experimental 
tissue. 
In the blood the identification of cells for obvious reasons is 
carried out under greater difficulties than elsewhere and tenta- 
tive non-histological terms, such as transitional leucocyte, large 
mononuclear leucocyte, etc., have been introduced. Had mor- 
phological characters been more closely defined these terms 
would have served a more useful purpose until such time as the 
origin of the cells could be established, but no uniformity exists 
in regard to the cells which are to be included under these terms. 
The number of observations on normal and pathological bone- 
marrow appears to warrant the statement as a fact that the 
neutrophiles, eosinophiles, and basophiles (polymorphonuclear 
leucocytes) differentiate from younger myeloblastic cells nor- 
mally present only in the bone-marrow. A _ parallel state- 
ment holds for the lymphocytes, and that the smallest cells of 
the blood come from the lymphoid tissue is not seriously 
questioned. There are present, however, non-lymphocytic mono- 
nuclear cells of a different type and these are larger than the 
lymphocytes and frequently have irregularities in the nuclear 
contour. It is about these that the greatest doubt exists. The 
significance of the experiments tabulated below calculated to 
show the origin of phagocytic non-lymphocytic mononuclear 
cells does not rest on the acceptance of any prescribed origin of 
lymphocytes or polymorphonuclear leucocytes (neutrophiles, 
eosinophiles, and basophiles), but is based rather on the speci- 
ficity of the function of phagocytosis by a given cell under given 
conditions. The only point urged here is that lymphocytes, 
eosinophiles, basophiles, fibroblasts, most epithelial cells, etc., do 
