i 
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invariably noted a most marked increase of the large mononuclear leuco- 
cytes and transitionals, and almost an entire absence of small lymphocytes. 
The counts in five cases which had been very carefully studied averaged 
as follows: 
Per cent. 
Polymorphonuclears 42 
Large mononuclears and transitionals 40 
Large lymphocytes 8 
Small lymphocytes 8 
Eosinophiles and mast cells 2 
In all these cases the counts were made after the appearance of the 
rash, the patient having been sent to the hospital about the time of the 
terminal rash. Subsequently, a patient who had been admitted with 
dysentery developed a temperature of 39.5° C. on the second day after 
his admission. Suspecting dengue, a blood count was immediately made 
and recorded as follows: 
Per cent, 
Polymorphonuclears 32 
Large lymphocytes 25 
Small lymphocytes 37 
Large mononuclears and transitionals 6 
After the appearance of the rash his differential count corresponded 
closely with the ones previously given. 
As opportunity occurred to examine several cases at the commencement 
of the disease, we were surprised to find in one, during the first day 
of illness, a count of 50 per cent of small lymphocytes, with very few 
large lymphocytes and scarcely any large mononuclears. Repeated exam- 
inations were made daily in this case and the leucocytes were found to 
vary markedly from day to day, so that by the fourth one there were only 
about 8 per cent of small lymphocytes, the latter having been replaced by 
the large mononuclears and large lymphocytes. 
When I refer to a small lymphocyte I mean the leucocyte which 
constitutes the characteristic element of lymphatic leukemia and which 
is largely made up of nucleus, with only a narrow or crescentic fringe of 
cytoplasm. As a result of my limited experience I believe it to be very 
probable that, should differential counts be made in a large series of 
cases, it would develop that the diminution in percentage of polymorpho- 
nuclears is largely replaced, during the first day, by small lymphocytes, 
subsequently, the large lymphocytes would replace the small ones and 
on about the fifth day, or at the time of the appearance of the terminal 
rash, it would be noted that large mononuclears and transitionals had 
taken the place of the lymphocytes. It is this almost kaleidoscopic 
change in differential count which is so characteristic of dengue and I 
do not know of any other disease in any degree presenting such a striking 
variation. 
It can readily be seen that the differential leucocyte count would be 
of very great value in the diseases which might specially be confounded 
