THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
by Ehrlich* present no difficulty. It is in the estimation of the non-granular, 
mononuclear elements that there is a lack of uniformity. The criteria by which 
various observers decide exactly to what class a doubtful cell belongs are not always 
the same. 
Although there are two, or perhaps three, well-marked 'types ' or mononuclear 
leucocytes, forms intermediate between them may occur. There is no definite 
characteristic by which such intermediate forms may be classified ; and in differential 
counts, as often presented, the personal equation is a regrettable factor. It is in an effort 
to avoid this personal error, and to present our work in a form which will have a real 
clinical value, that we have grouped our mononuclear elements in the manner here 
described. 
The deeply basophile lymphocyte of about the same size as a red cell, with 
deeply staining cytoplasm and central, relatively large, nucleus is a constant, easily 
recognizable type. It must be remembered that, though forms are often seen whose 
protoplasm is not more basophile than their nuclei, yet these cells possess every other 
characteristic of small lymphocytes, and as such they must be classified. A study of 
a sufficient number of films will lead from these small forms, by insensible gradations, 
through a long series of mononuclear cells to a type of leucocyte possessing all the 
characteristics of a ' large mononuclear.' 
The typical large mononuclear leucocyte, as described by Ehri.ich (/or. «'/.), 
occurs in normal blood in very small numbers (one per cent.) and is also a constant 
easily recognizable form. It is a huge cell, two to three times the size of a red cell, 
and possessing a relatively large amount of usually palely staining cytoplasm and an 
oval eccentrically placed nucleus. The cytoplasm is finely, the nucleus coarsely, 
reticulated. t 
Between these two extremes there is an intermediate group of cells possessing 
characteristics which do not conform to those of either division. 
Many observers, however, do not strictly hold to Ehrlich's definition of a 
' large mononuclear leucocyte,' but classify under this head almost any cell which is 
slightly larger than a lymphocyte, possessing at the same time the staining reactions, 
structure, and often bean-shaped nucleus of a 'large mononuclear.' By so doing 
they avoid a complex classification. It is the difficulty of determining exactly what 
combination of properties is sufficient to place members of this large unclassified 
group into either of the two main divisions which has produced a third class ' large 
lymphocyte.' The nuclei of any ot these mononuclear cells may be ' incurved,' 
' horseshoe shaped,' or even sub-divided. 
Cells of the small lymphocyte type with irregular nuclei (rarely 0*5 per cent, 
in normal blood) are classified as lymphocytes. Cells of the large mononuclear type 
* iihrlich u nd Lazarus. On- Anaemic, Wien, 1898. 
■f Ewiny, Clinical Pathology of the Hood, 1901. 
