1908. | Innervation in Vaso-motor Reflexes, etc. 345 
The tongue, especially in the dog, would be expected to be a favourable 
organ for investigation of vascular reflexes. To my disappointment it was 
- found to give very poor plethysmographic records, so far as concerns changes 
in its own vessels of an active nature. On excitation of the central end of 
depressor or vagus there was occasionally to be seen a slight dilatation at the 
beginning of the fall of pressure, but this was soon overpowered by the 
passive effect of the lowered arterial pressure. In these experiments the 
cervical sympathetics were cut on both sides, so that the tongue was supplied 
only with vaso-dilators. 
In the course of experiments made for another purpose two or three years 
ago, I noticed that in a depressor reflex, the abdominal sympathetics having 
been cut, there was increase of volume of the penis, enclosed in a plethysmo- 
graph. Since the rhythmic contractions shown by the curve were also 
inhibited, it might be that these contractions, probably due to the retractor 
penis, were responsible for the changes of volume. I have recently, 
therefore, repeated the experiment, three times in all. 
In the first experiment, although there was a marked effect, it was found, 
post mortem, that only one of the sympathetics had been completely severed, 
the other was merely crushed. This latter was apparently incapable of 
conduction, since there was no contraction of the organ on excitation of a 
sensory nerve nor in asphyxia. 
In the second experiment the vaso-dilatation did not appear until the 
arterial pressure had returned to its original level, so that it might be due 
to local reaction. This does not seem to have been the case, however, since 
an equally great and sudden fall produced by cardiac inhibition was not 
followed by any dilatation. 
Fig. 2 was obtained in the third experiment. After a long latent period 
the blood-pressure begins to fall, and simultaneously there is an increase of 
volume of the penis. The curve has the appearance of having been cut off 
at the top; this is, no doubt, due to the piston recorder sticking slightly at 
this position. 
The conclusion to be drawn is that when cut off from the vaso-constrictor 
centre the penis is still capable of reflex vascular dilatation, which can only 
be due to excitation of vaso-dilator nerves contained in the pelvic nerves of 
Langley, the nervi erigentes of Eckhard. 
It was shown by Winkler,* with some degree of probability, that vaso- 
dilators to the external ear of the rabbit run in upper cervical nerve-roots. 
They are, perhaps, posterior root fibres, and, if so, the dilatation is antidromic 
in nature. The majority of the constrictor fibres run in the cervical 
* ‘Sitzungsberichte d. Wien Akad.,’ Math.-Naturw. Klasse, vol. 111, June, 1902. 
