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676 GENERAL PATHOLOGY. ;
their further discussion will be taken up in connection with that
subject.
It is to direct experimentation through vivisection that we are in-
debted for our knowledge of the phenomena of hypersemia in its simple
and uncomplicated forms, and indeed for what knowledge we possess of
the vaso-motor system of nerves. There are no anatomical differences
existing in the nervous system by which we can know a motor from a
sensory nerve. By means of vivisection, then, the vaso-motor nerves
are found to emanate from the spinal cord with the posterior or sensory
roots of the spinal nerves, and pass to the sympathetic system by way
of the rami covimunicantcs. Ai'ter passing some distance, up or down
as the case may be, with this system, they again join the spinal nerves
in communicating branches, and pass to the extremities in company
v/ith the motor and sensory nerves of these parts. When hyper^emia
is produced directly by severing the vaso-motor nerves, it presents the
following phenomena : The parts become somewhat swollen and red-
dened by the entrance of a greater amount of blood into them, and at
the same time the temperature is markedly elevated. The elevation of
temperature, however, in the most intense hyperaemia that can be pro-
duced never quite reaches that of the central portions of the body
indeed, it may be accounted for in all cases by the increased amount of
warm blood passing through the circulatory apparatus. This process,
when excited in this way i c. by interference with the vaso-motor
nerves—never leads to inflammation. It seem-s to have relation solely
to the state of the blood-vessels, which are simply widely dilated, ad-
mitting a larger quantity of blood. If the induced hypersemia be of
large extent the immediate effect is to reduce the general blood-pressure;
but this is cjuickly regained, unless there are other reasons for depres-
sion. The blood-pressure seems to have little to do with the state of
hyperpemia, for it is no greater in the hypersemic part than elsewhere.
Indeed, it may be actually less, for the reason that the blood is less
hindered in its passage to the venous system, there seeming to be an
expansion of the capillaries as well. Owing to the increased diffused
redness this is well seen in any parts that are sufficiently transparent.
We can now understand why we have a collateral hypersemia after
the ligation of an artery. If the carotid artery be tied, the corre-
sponding vessel of the opposite side becomes expanded. This is not to
be explained by increase of the blood-pressure caused by the stoppage
of the flow through tlie artery ligated, for such increase of pressure
would be either general or in the arteries most directly connected with
the ligated branch. This is not the case. The expanded artery is the
one that can most directly su})j)ly the territory deprived of blood by
the ligation. This is a reflex phenomenon, taking place through the
action of the vaso-motor nerves in response to the needs of certain tis-
sues for blood. This is the type of the reflex phenomena of the vaso-
motor nerves in all cases of this character. Increased quantities of
blood are, through these reflex actions, called to special parts or terri-
tories of the circulation under a great variety of circumstances of which
some have already been indicated. If the hands are smartly struck
together a few times, a reponse in the form of increased redness will be
676 GENERAL PATHOLOGY. ;
their further discussion will be taken up in connection with that
subject.
It is to direct experimentation through vivisection that we are in-
debted for our knowledge of the phenomena of hypersemia in its simple
and uncomplicated forms, and indeed for what knowledge we possess of
the vaso-motor system of nerves. There are no anatomical differences
existing in the nervous system by which we can know a motor from a
sensory nerve. By means of vivisection, then, the vaso-motor nerves
are found to emanate from the spinal cord with the posterior or sensory
roots of the spinal nerves, and pass to the sympathetic system by way
of the rami covimunicantcs. Ai'ter passing some distance, up or down
as the case may be, with this system, they again join the spinal nerves
in communicating branches, and pass to the extremities in company
v/ith the motor and sensory nerves of these parts. When hyper^emia
is produced directly by severing the vaso-motor nerves, it presents the
following phenomena : The parts become somewhat swollen and red-
dened by the entrance of a greater amount of blood into them, and at
the same time the temperature is markedly elevated. The elevation of
temperature, however, in the most intense hyperaemia that can be pro-
duced never quite reaches that of the central portions of the body
indeed, it may be accounted for in all cases by the increased amount of
warm blood passing through the circulatory apparatus. This process,
when excited in this way i c. by interference with the vaso-motor
nerves—never leads to inflammation. It seem-s to have relation solely
to the state of the blood-vessels, which are simply widely dilated, ad-
mitting a larger quantity of blood. If the induced hypersemia be of
large extent the immediate effect is to reduce the general blood-pressure;
but this is cjuickly regained, unless there are other reasons for depres-
sion. The blood-pressure seems to have little to do with the state of
hyperpemia, for it is no greater in the hypersemic part than elsewhere.
Indeed, it may be actually less, for the reason that the blood is less
hindered in its passage to the venous system, there seeming to be an
expansion of the capillaries as well. Owing to the increased diffused
redness this is well seen in any parts that are sufficiently transparent.
We can now understand why we have a collateral hypersemia after
the ligation of an artery. If the carotid artery be tied, the corre-
sponding vessel of the opposite side becomes expanded. This is not to
be explained by increase of the blood-pressure caused by the stoppage
of the flow through tlie artery ligated, for such increase of pressure
would be either general or in the arteries most directly connected with
the ligated branch. This is not the case. The expanded artery is the
one that can most directly su})j)ly the territory deprived of blood by
the ligation. This is a reflex phenomenon, taking place through the
action of the vaso-motor nerves in response to the needs of certain tis-
sues for blood. This is the type of the reflex phenomena of the vaso-
motor nerves in all cases of this character. Increased quantities of
blood are, through these reflex actions, called to special parts or terri-
tories of the circulation under a great variety of circumstances of which
some have already been indicated. If the hands are smartly struck
together a few times, a reponse in the form of increased redness will be
