PAR VAGUM. \_ 
however, the respiration has been suspended 
for a longer time and venous blood begins to 
circulate along the arteries, the other excitants 
of the besoin de respirer come into operation. 
Brachet,* Krimer,t and Longet,f have from 
their experiments arrived at the conclusion that 
the sensations occasioned by irritation of the 
inner surface of the trachea and bronchial tubes, 
and which usually precede coughing, are anni- 
hilated by dividing the vagi. We have made 
repeated experiments on this point, and though 
we could not satisfy ourselves that these sensa- 
tions were affected to the extent maintained by 
these authors, we believe that they are at least 
blunted. 
To what extent do the filaments of the vagi 
act as incident nerves ?—It has been proved by 
_ the experiments of Legallois,§ Flourens,|| and 
| others, that all the respiratory and muscular 
movements cease on destroying the medulla 
oblongata, though the other parts of the ence- 
phalon situated above this may be injured in 
various ways without necessarily producing 
this effect. Itis further well known that if the 
Spinal chord be cut across, all the respiratory 
muscles are paralysed which receive their 
nerves from that portion of it below the point 
where it was divided, while those muscles 
which receive their nerves from that portion of 
the spinal chord still continuous with the me- 
dulla oblongata perform their usual functions. 
From these and other facts it may be consi- 
dered as ascertained that all impressions made 
at the lungs and elsewhere capable of causing 
respiratory movements, must be conveyed to 
the medulla oblongata before they can produce 
any reflex excitation of the muscles of respira- 
tion. That the vagi can convey these impres- 
sions from the lungs is not only rendered pro- 
bable from their attachment to the medulla 
oblongata, but may almost be considered as 
proved by the result of the experiments upon 
the spinal chord to which we have just referred. 
It, however, by no means follows that the vagi 
are the sole excitant nerves of respiration. It 
has been fully ascertained by numerous expe- 
rimenters, more especially by those who have 
investigated the functions of this nerve from the 
time of Legallois, that an animal will continue 
to breathe after the division of both vagi in the 
neck, if care be taken to secure the ingress and 
egress of air to and from the lungs. It is now 
' well known, as we have already had occasion 
to point out in examining the functions of the 
laryngeal branches, that if the vagi be injured 
_ above the origin of the recurrent laryngeals, 
none of the muscles attached to the arytenoid 
cartilages can any longer act in unison with the 
| muscles of respiration, all their movements 
_ cease, and the superior aperture of the larynx 
| can no longer be dilated during inspiration. 
If the larynx be large, and the animal refrain 
_ * Oper. cit. p. 157-8-9. 
3 ee agen iiber den Husten, as quoted by 
uller, 
m) t Oper. cit. tom. ii. p. 289. 
g ' Sur le Principe de la Vie. 
_ || Recherches Expérimentales sur les Proprietés 
t les Fonctions du Systéme Nerveux, &c. Paris, 
t VOL. III. 
897 
from any violent effort, an adequate quantity of 
air may still find its way to the lungs, and the 
respirations are at first performed with ease. 
If, on the other hand, the larynx be small, its 
superior aperture may be ‘mechanically closed 
and the animal may be immediately suffocated, 
or the air may still pass through the larynx but 
in diminished quantity, and the animal may 
labour under dypsneea from the moment the 
nerves are divided, up to its death. Even when 
means are taken to secure the free entrance of 
air into the lungs, an immediate and marked 
diminution in the frequency of the respiratory 
movements follows the division of both vagi 
in the neck. A.G.F. Emmert concluded, but 
apparently more upon theoretical grounds than 
from any direct observations made in the two 
experiments he had at that time performed on 
rabbits, that after lesion of the vagi the respira- 
tions become less frequent and prolonged.* 
Mayer reckoned the number of respirations, 
both before and at various periods after section 
of these nerves in five experiments upon the 
ass, dog, and rabbit, and found a very marked 
diminution in their frequency after dividing the 
nerves.t Mr. Broughton mentions, that in a 
horse in which the vagi were divided “ the 
respirations became slow, twelve in a minute ;” 
and in another horse “ the respirations fell to 
five in the minute.”{ At what period after 
the division of the nerves these last observations 
were made, and what was the number of the 
respirations previous to the commencement of 
the experiments, we are not informed. Sir 
Astley Cooper has given the result of two expe- 
riments upon rabbits which well illustrate the 
effect of the division of the vagi upon the respi- 
ratory movements.§ In our experiments we 
ascertained that the diminution in the frequency 
of the respiratory movements, generally to less 
than half of their former number, is an imme- 
diate effect of thedivision of both vagi. Therespi- 
ratory movements seem to be performed more 
slowly, and, generally, even from the first, in a 
somewhat heaving manner.|| Arnold in his expe- 
riments upon hens also observed a very consi- 
derable diminution in the frequency of the re- 
spiratory movements.f] Brachet has asserted** 
that an animal continues to breathe after sec- 
tion of the vagi, because it has acquired the 
habit of using the respiratory muscles. Dr. 
Marshall Hall has maintained that after the 
vagi are divided the respiratory movements are 
no longer a function of the excito-motory but 
of the cerebral portion of the nervous system ;++ 
* Archiv. fiir Physiologie von Reil und Auten- 
rieth, Neunter Band. 1809, s. 417. 
+ Tiedemann’s Zeitschrift fiir 
Zweiter Band, 1826, s. 77. 
¢ Quarterly Journal of Literature, Science, &c. 
vol. x., p. 305 and 307. 
fa Hospital Reports, No. 3, Sept. 1836, 
- 409. 
Physiologie, 
: || Transactions of British Scientific Association 
for 1838, and Edin. Med. and Surgical Journal for 
1839, vol 51. 
§ Bemerkungen tiber den Bau des Hirns und 
Riickenmarks, &c. s, 148. Zunch, 1838. 
** QOper. cit. p. 132. 
t+ Philosophical Magazine for Jan. 1835, Lee- 
3M 
