EXPERIMENTS ON THE CENTRAL END OFTHE PNEUMOGASTRIC NERVE.

(Preliminary Communication.)

BY J. ALFRED SCOTT, L.R.C.S.;Lecturer on Physiology, Carmichael College, Dublin.

[Read in the Sub-Section of Anatomy and Physiology, December 6, 1883.]

DURING the past summer, while performing some experiments at

the laboratory of the Carmichael College, in association with Dr.

Purser, on the connexion between the stimulation of certain nerves

and blood pressure, our attention was directed to the central end

of the divided pneumogastric, and as some of the results were so

constant, yet differing from the experience of other observers,

I may be pardoned for occupying the time of this Sub-Section of

the Academy.

The ordinary text-books give but little information relative

to the effects of stimulation of the central end of the vagi,

and that little seems involved in some doubt, but the main facts

which bear on the present communication may be summed up as

follows :-

1. Quickening of the respiratory movements if weak stimuli

be employed.

2. Tetanus of same if strong stimuli.

3. Diminished blood pressure if stimuli be applied above junc-

tion of the depressor nerve.

4. Slowing of the heart-beat if other vagus be intact.

The animals used in our experiments were all rabbits, anas-

thetised with chloral hydrate, the cannula being inserted in thecarotid artery, and a Marey's pneumograph placed outside thethorax.

Central End of the Pneumogastric Nerve. 493

The stimuli were all strong induction shocks from Du Bois

Reymond's apparatus, secondary coil at from 15-8 mm., and was

applied below the origin of the depressor nerve.

When only one vagus was divided, and the central end stimu-

lated, there was a slight fall of pressure (about 2-3 mm.), due

probably to dilation of peripheral arterioles, but there was no

slowing of the heart-beat.

On section of the other vagus and again stimulating, there was

a considerable rise of pressure (upwards of 10 mm.), which was

accompanied by a very remarkable class of heart-beats, sometimes

during the stimulus and sometimes after it ceased. These beats

were of considerable amplitude, and occupied fully twice the length

of time of the normal beat.

Associated with these phenomena was the cessation of respira-

tion mentioned above, which was invariably followed by expiration

when one nerve was intact, and by inspiration when both were

divided.

In order to settle whether the simple stoppage of the respiration

affected the heart through the blood current, we opened the trachea

and inserted a cannula, through which respiration was subsequently

carried on.On closure of this cannula the lungs were necessarily deprived

of air, and the blood-pressure rose; but in no case was the heart-

beat slowed, or were any appearances such as were described

above found on the tracing.

These observations would seem to show that there is some other

inhibitory channel than the vagi by which the heart can be

affected. The form of the beats differs extremely from the

tracings of a peripheral stimulus, considering that the heart is

never stopped but only slowed, and that there is an increase instead

of a fall in the blood-pressure.

The question naturally arises---Through what channel do these

inhibitions pass; is it through sonne yet undescribed nerve, or is

it due to a central action, modifying or destroying the action of

the 11 accelerator " nerves `2

To settle these points, further experiments are necessary, not

494 Central End of the Pizeurnogastric Nerve.

only on different animals but under different conditions of anaes-thesia ; but in the meantime I would be glad of any assistance inthe two facts mentioned

1. Inhibition of heart by other channel than. vagus.2. Tetanus of respiratory muscles followed by

a. One vagus, cut - - - Expiration.b. Both „ „ - - - Inspiration.