The total quantity of blood is raised. While increased in quantity, the
blood appears on the whole to be somewhat depreciated in quality, though
on this point there are considerable differences of opinion. Thus, as
regards haemoglobin, some investigators have found that the old idea as to
the poverty of haemoglobin in pregnancy is quite unfounded; a few have even
found that the haemoglobin is increased. Most authorities have found the
red cells diminished, though some only slightly, while the white cells,
and also the fibrin, are increased. But toward the end of pregnancy there
is a tendency, perhaps due to the establishment of compensation, for the
blood to revert to the normal condition.[177]
It would appear probable, however, that the vascular phenomena of
pregnancy are not altogether so simple as the above statement would imply.
The activity of various glands at this time--well illustrated by the
marked salivation which sometimes occurs--indicates that other modifying
forces are at work, and it has been suggested that the changes in the
maternal circulation during pregnancy may best be explained by the theory
that there are two opposing kinds of secretion poured into the blood in
unusual degree during pregnancy: one contracting the vessels, the other
dilating them, one or the other sometimes gaining the upper hand.
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