or precede a change of
weather from dry to wet, from a low to a high barometric pressure.

Costiveness, which is the usual concomitant of fever, may in a case of this
kind become an accessory cause, the retention in the blood of what should
have passed off by the bowels tending to increase the fullness of the blood
vessels and the density of the blood.

Mature age is a very strong accessory cause. The disease never occurs with
the first parturition, and rarely with the second. It appears with the
third, fourth, fifth, or sixth--after the growth of the cow has ceased and
when all her powers are devoted to the production of milk.

Calving is an essential condition, as the disturbance of the circulation
consequent on the contraction of the womb and the expulsion into the
general circulation of the enormous mass of blood hitherto circulating in
the walls of the womb fills to repletion the vessels of the rest of the
body and very greatly intensifies the already existing plethora. If this is
not speedily counterbalanced by a free secretion from the udder, kidneys,
bowels, and other excretory organs, the most dire results may ensue.
Calving may thus be held to be an exciting cause, and yet the labor and
fatigue of the act are not active factors. It is after the easy calving,
when there has been little expenditure of muscular or nervous energy and no
loss of blood, that the malady is seen. Difficult parturitions may be
followed by metritis, but they are rarely connected with parturition fever.

All these factors coincide in intensifying the one condition of plethora
and point to that as a most essential cause of the affection. It is
needless to enter here into the much-debated question as to the mode in
which the plethora brings about the characteristic symptoms and results. As
the results show disorder or suspension of the nervous functions mainly, it
may suffice to say that this condition of the blood and blood vessels is
incompatible with the normal functional activity of the nerve centers. How
much is due to congestion of the brain and how much to bloodlessness may
well be debated, yet in a closed box like the cranium, in which the
absolute contents can not be appreciably increased or diminished, it is
evident that, apart from dropsical effusion or inflammatory exudation,
there can be only a given amount of blood; therefore, if one portion of the
brain is congested, another must be proportionately bloodless; and as
conge