THE CIRCULATION OF THE BLOOD. 7 
especially in gunshot and other wounds involving nerves, that 
vaso-motor effects have followed. 
4, Section of certain nerves, as the nervi erigentes of the 
penis, is not followed by dilatation; but these nerves and the 
chorda tympani supplying the salivary gland are examples of 
so-called vaso-dilators, inasmuch as their stimulation gives rise 
to enlargement of the caliber of the arterioles in their area of 
distribution. 
5. On the other hand, such a nerve as the cervical sympa- 
thetic, as may be readily shown in the rabbit, when its periph- 
eral end is stimulated, gives rise to constriction, and hence is 
termed a vaso-constrictor. 
6. When, however, the divided sciatic nerve is stimulated 
peripherally, the result may be either constriction or dilata- 
tion. 
7%, When the spinal cord of an.animal is divided across, 
there is vascular dilatation of all the parts below the section 
(loss of arterial tone); but in time the vessels return to their 
usual size (restoration of arterial tone). 
8. On destruction of a certain minute portion of the medulla 
oblongata, there is a general loss of arterial tone. This area 
(center) extends in the rabbit from a short distance below the 
corpora quadrigemina (1 to 2 mm.) to within 4 to 5 of the 
calamus scriptorius, as ascertained by the effects on the vessels 
of cutting away the medulla in thin transverse sections. At 
the spot indicated there is a collection of large multipolar 
nerve-cells (antero-lateral nucleus of Clarke). 
Conclusions.—1. There ‘are vaso-motor nerves of two kinds— 
vaso-constrictors and vaso-dilators—which may exist in nerve- 
trunks either alone or mingled. 
Examples of the former are found in the cervical sympa- 
thetic, splanchnic, etc., of the latter in the chorda tympani, 
nerves of the muscles and nervi erigentes (from the first, second, 
and third sacral nerves), while the sciatic seems to contain 
both. 2. Impulses are constantly passing from the medullary 
vaso-motor center along the nerves to the blood-vessels, hence 
their dilatation after section of the nerves. 
The nerves are traceable to the spinal cord, and in some 
part of their course run, as a rule, in the sympathetic system. 
3. Impulses pass at intervals to the areas of distribution of 
vaso-dilators along these nerves, the effect of which is to dilate 
the vessels through their influence, as in other cases, on the 
muscular coat. 
