rge mononuclear cells is
observed in the post-febrile stage of measles.

On the grounds merely of microscopical investigations we conclude that
the bone-marrow is by far the most important of the blood-forming
organs, for its function is the exclusive production of red blood discs
as well as of the chief group of the white corpuscles, the polynuclear
neutrophil.

=The physiological, experimental investigation= of the functions of the
bone-marrow offers insurmountable difficulties. An exclusion of the
whole bone-marrow or of larger portions only is an impossible operation.
Nor can we ascribe any value to the researches which endeavour to obtain
a result by comparative enumerations of the arterial and venous blood of
a bone-marrow area. J. P. Roietzky working under Uskoff's direction has
recently made counts of this kind in the dog, from the nutrient artery
of the tibia and the corresponding vein. He found that the number of
white corpuscles of the vein is slightly greater, that on the other hand
the absolute number of "young corpuscles" (Uskoff), _i.e._ of the
lymphocytes, has been considerably diminished, whilst the number of
"ripe" corpuscles, which for the most part correspond to our
polynuclear, is considerably increased. He gives the following table:

-------------------------------------------------------------
Total number | Young | Ripe | Old
| corpuscles | corpuscles | corpuscles
-------------------------------------------------------------
Arterial blood 15000| 1950 (13%) | 840 (5.6%) | 12210 (81%)
Venous " 16400| 656 (4.0%)| 2788 (17.0%)| 12956 (79.0%)

The argument based on figures such as these assumes that the function of
the bone-marrow is =continuous=; an assumption which Uskoff indeed seems
to make.

But if the bone-marrow is constantly absorbing the lymphocytes to such
an extent, it is quite incomprehensible how the normal condition of the
blood can be preserved, bearing in mind the extent of the bone-marrow
and the rate of the circulation. All evidence indeed tends to shew that
on the contrary the bone-marrow performs its functions discontinuously,
inasmuch as elements continually grow to maturity in the bone-marrow, as
we have above explained, but they only emigrate at certain times as the
result of chemical stimuli. It is obvious _a priori_ from this
consideration how inconclusive must be the results of experiments such
as these of Roietzky[17].