d medulla oblongata. When
the spinal cord is divided, the vessels are cut off from the influence
of this vaso-motor centre, and at once dilate, profoundly affecting the
blood-current by doing so.

The first fall of temperature which follows division of the cord is
believed by most physiologists to be due to this dilatation of the
vessels. Very probably the blood-stream, flowing sluggishly, does not
give the normal amount of stimulus to the tissues, so that at first
their chemical actions are lessened, and consequently less caloric than
usual is generated in the body. Further, the blood moving slowly through
the dilated vessels of the lungs and of the surface of the body, is
cooled more completely than it should be; hence, unless the body is
protected by being surrounded with warm air, no excessive accumulation
of heat in it can occur, and therefore no fever can appear.

Assuming that this explanation of the primary lowering of the
temperature after division of the cord be correct--and no better one has
as yet been offered--what is the cause of the fever which afterward
develops itself? As it occurs only when the animal is exposed to a
somewhat elevated temperature, it has been thought by some to be due to
the absorption of this external heat. This, however, is certainly not
true, as is shown, to omit less decisive proofs, by the experiments of
Naunyn and Quincke, who exposed animals for two days to a temperature of
90 deg., and at the end of that time, their bodily temperature not having
risen, cut their spinal cords, after which intense fever was developed
in a few hours without any change of atmosphere.

Section of the cord must therefore give rise to an increased chemical
movement and heat-production in the body. As already stated, this
section affects very greatly the circulation, but the fever is
independent of such action. The upper end of the medulla oblongata is
continuous with a nervous mass which joins the two brain hemispheres
together, and hence is known as the _pons_ or bridge. If, instead of
cutting the spinal cord, we separate the medulla oblongata from the
pons, an _immediate_ rise of temperature occurs, and continues until
death, whether the operation be performed in a cold or heated room.[3]

Cutting the medulla at its junction with the pons causes, then, an
immediate and direct elevation of temperature, without disturbance of
the circulation. What can this mean? Evidently, only one thing--namely,