than 0 . 05 of a litre ,
a possible volume error of at the most
3 ml .of methane per five minutes i s considered t o be low enough t o be
ignored.
121
( e ) in
Based on the work of Bergman �nd Dukes
( 1926) ,
who acknowledgedthe investigations of Toussaint
(1875 ) ,
Colin( 1871 )
and Fluorens(�844),
the generally a ccepted current theory of regurgitation is that a quick inspiratory effo�' with a closed glottis leads to a sharp fall in intrapulmonary pressure with the lungs tending tocontract towards the rigid walls of the " costal box" . This in turn
i s believed to create a negative pressure within the thoracic
oesophagus causing it to dilate and so allow the highly fluid
rumen contents to siphon rapidly through the relaxed cardia when
it is transported to the fauces by its own momentum aided by an
anti-peristaltic wave in the oesophageal wall .
Bergman and Dukes
(1926)
found that breathing and mastication are interrupted for several seconds at the time of regurgitation and that there was no increase in chest movement or rectal pressure and only a small and apparently insignificant momentary increase in intra-ruminal pressure. On the otherhand
a small cannula inserted into the trachea and attached to a recording manometer shot-Ted asharp fall in intra-tracheal pressure at the moment of regurgitation. By using
an
animal with an established �en fistula they were able to demonstrate, by direct examination, that a negative pressure occurred at the cardia at the instant of regurgitation. Dukes( 1955 )
states , " • • • in regurgitation the entrance of food into the oesopha s i s brought about by intra-oesophageal negative pressuredue to an inspiratory effort with a closed glottis." He also quotes Kryzwanek
(1934)
asan
authority for the statement that ruminants with pneumothorax or an opening into the trachea are unable to regurgitate or do so only with difficulty.122
Another modern worker. Stigler
(1931 ) .
also investigated the mechanism of rumination and reviewed earlier theori�s paying par ti cular attention to those of Toussaint . Colin 1 Wester and Mangold .According to the above worker . Chauveau and Toussaint took the view that the entrance of the ingesta into the oesophagus is accomplished by an inspiratory effort with a closed glottis .
Colin is credited with the belief that the oesophagus relaxes with regurgitation and forms a funnel shaped widening into which the half fluid forestomach contents stream. The same author writes .
Wester's theory was that the oesophagus sucks up the regurgitate
by its active widening without the inspiratory fall in pressure being necessary. He believed that the cardial opening occurs when the diaphragm first contracts while simultaneously the circular muscle ring in the caudal part of the oesophagus is relaxed and that the oesophagus contracts in its entire length. Thus the posterior end of the oesophagus must be widened. The opening of the cardia
is.according to Wester. assisted by a tretching of the stomach
wall round the cardia .
Stigler lists Mangold as the originator of the theory that primarily no significant activity of � organ may be necessary
12j
to cause the ruminating mass to go from the forestomach to the oesophagus as s oon as the cardia opens . According to the greatest quantity of water giving sufficient difference in hydrostatic pressure to bring food into the oesophagus on opening of the cardia is
10
to15
cm . in the goat, and as one can see clearly in X-rays , the opening of the oesophagus into the stomach ( in the standing animal)
lies deeply under the level of the rumen contents and under the air bubble in the food . Stigler comments that transport of the regurgitate by hydrostatic pressure alone is comparatively slow whereas in X-rays one sees that the ruminating mass is conveyedat great speed from the cardia through the cervical oesophagus to
the neck . Stigler considered that this speed is brought about by a force derived from : -
(1 )
Greater pressure in the forestomach following its activecontraction , or by abdominal pressure.
( 2 )
Decrease of the pressure in the oesophagus either byinspiratory lowering of the intra-thoracic pressure, or through active widenin of the oesophagus.
After a lengthy investigation, Stigler ives the following s equence of events as his explanation of how regurgitation takes place and comments that the mechanism of insuction described cor responds to the theory of Chaveau and Toussaint.
( 1 )
Rumination begin as a rule with the swallowing of saliva .,
oral parts of the thoracic oesophagus , apparently in order to press out swallowed air .
( J ) The glottis closes and the insuction phase begins.
(4 )
The diaphragm makes a backward inspiratory movement.( 5 )
A t the same time the head and neck are flexed more or less dorsally. Thi s has the object of improving the closure of the cervical oesophagus and hindering the jnsuction of airfrom the mouth into the thoracic oesophagus.
( 6 )
Following the fall in the intra-thoracic pressure brought about by the inspiratory movement with a closed glottis, the thoracic oesophagus is sucked open and a decrease of pressure occurs inside it .( 7 )
S�muJ tanoously the cardia opens.( 8 )
Some of the rumen and reticulum contents, mostly as a fluidbroth , are sucked up into th� oesophagus by the negative pressure
in the thorax and thoracic oesophagus and are carried by an anti-peristaltic wave to the mouth .
As objections against the acceptance of this theory, Stigler
notes that it is said , rumination can still take place after :
(1 )
The cutting of both phrenic nerves(2)
Tracheotomy( J ) Pneumothorax
He states however, that these objections are not acceptable for the following reasons : -