(1) The eructation reflex in sheep and cattle, and factors affecting it, have been
studied mainly by the method of forced air insufflation and direct recording
of intraruminal pressure.
(2) Eructation is a complex, co-ordinated reflex involving the rumen, reticulum,
cardiac orifice and the oesophagus. It consists essentially in the movement of free
gas from the dorsal rumen, forwards and downwards to the cardia. This is
(a) A forward wave of contraction of the ruminal musculature (as distinct
from the usual backward cycle of contractions).
(b) Opening of the cardiac orifice which is brought about by contraction
of the lateral and medial pillars of the rumino-reticular fold .
(c) The clearing of the cardia of fluid ingesta is affected by relaxation of
the reticulum. The relative importance of this phase depends on the
degree of filling of the rumen.
(3) The main stimulus for eructation is gas pressure in the posterior dorsal
sac of the rumen.
(4) From variations amongst the individual experimental animals it is
believed that the efficiency of the reflex may depend on hereditary factors.
(5) The factors affecting the reflex are: -
(i) Obstruction of the oesophagus.
(ii) Frothing of the ingesta.
(iii) The degree of filling of the rumen and posture. Overfilling of
the rumen was found to hinder eructation by increasing the
distance between the free gas and cardiac orifice. Elevation
of the hindquarters had a similar effect, while elevation of the forequarters mitigated the effects of overfilling. Animals with
a non-functioning reticulum were found to be particularly
susceptible to overfilling.
In the absence of other factors, the efficiency of eructation was
found to vary inversely with the degree of alkalosis as determined
by the CO₂-combining power of the blood. This was due mainly
to reticular paralysis.
C. Abdominal Vagotomy.
Section of the right ventral branch of the vagus caused
abomasal distension and chronic tympany, again due mainly to
inhibition of reticular activity. Section of the left dorsal branch
diminished the strength of ruminal contractions and eructation
efficiency for the first three weeks with subsequent partial recovery.
D. Reflex inhibition from the Posterior Digestive Tract.
Distension of both the abomasum and caecum reduced the
eructation efficiency again by inhibition of the reticulum.
E. The effect of Drugs influencing Ruminal Motility.
(a) Small doses of prussic acid inhibited the reticulum and
backward movement of the rumen with consequent
inefficiency of eructation and abolition of the reflex.
(b) Atropine, histamine and adrenaline were found to inhibit
the reflex completely even before a total paralysis of the
rumen was induced.
Carbamylcholine and veratrine both cause spasm of the
rumen and reticulum with consequent interference with
eructation. Their therapeutic use is contraindicated.