swallowing of the re-chewed material. Associated with this chain of events is

Transcription

1 43 J. Physiol. (I959) I49, STIMULATION AND INHIBITION OF RETICULUM CONTRAC- TIONS, RUMINATION AND PAROTID SECRETION FROM THE FORESTOMACH OF CONSCIOUS SHEEP BY R. W. ASH AND R. N. B. KAY From the Rowett Research Institute, Bucksburn, Aberdeenshire (Received 3 April 1959) In recent years there has been a renewed interest in the process of rumination, the essential features of which are the regurgitation of digesta, mastication and swallowing of the re-chewed material. Associated with this chain of events is a change in the pattern of reticulum contractions and an increase in parotid secretion. The stimulus to rumination under normal conditions is not known, but Schalk & Amadon (1928) found that mechanical stimulation of the forestomach usually initiated the process and this has been confirmed -more recently (Downie, 1954). Bell (1958) has suggested that rumination may be related to the concentration of circulating fatty acids, although there is no direct evidence for this hypothesis. Reflex control over reticulo-rumen contractions and parotid secretion, through stimuli acting in the forestomach and oesophagus, has been studied in anaesthetized and decerebrate sheep, goats and calves (Clark & Weiss, 1952; Comline & Kay, 1955; Kay & Phillipson, 1957; Comline & Titchen, 1957; Titchen, 1958; Kay, 1958). However, rumination does not occur under anaesthesia nor after decerebration. In the-experiments reported in this paper mechanical and chemical stimuli have been applied to the forestomach and oesophagus of conscious sheep fitted with a large-diameter rumen cannula, and the areas have been defined which, when stimulated, cause rumination, changes in motility of the reticulum and salivary responses. A preliminary account of these experiments has already been presented (Ash & Kay, 1957). METHODS Surgical. Access to the interior of the reticulo-rumen was gained through a 9 cm diameter cannula inserted into the dorsal sac of the rumen; the design of the cannula and the method of insertion have been described previously (Ash, 1957). Six Greyface and Cheviot sheep weighing kg were used for the operation and their experimental life ranged from 2 to 14 months.

2 44 R. W. ASH AND R. N. B. KAY At least 3 weeks elapsed between the operation and the first experiment. Recovery from the operation was always good, although some loss of body weight occurred during the first three postoperative weeks; thereafter body weight was maintained. The daily diet consisted of 500 g dried grass or hay and 250 g cereals. Five to seven months after the insertion of the cannula, silver electrodes shielded in polythene (Dziuk & Sellers, 1955) were applied in a second operation either to the dorsal, the ventral or both trunks of the thoracic vagus nerve about 5 cm anterior to the diaphragm in three sheep. The day before an experiment one parotid duct was cannulated through its papilla. The cannula consisted of a 20 cm length of polythene tube, diameter 1-5 mm, bore 1-0 mm (Sterivac cannula, Allen & Hanbury), slightly dilated at the tip and moulded to a suitable shape in hot water. The sheep was anaesthetized with pentobarbitone sodium (Nembutal; Abbott Laboratories) injected intravenously and one parotid papilla was dilated with a probe. The cannula, stiffened with wire, was inserted into the parotid duct for about 4 cm so that its tip lay on the surface of the masseter muscle; the wire was then withdrawn. The free end of the cannula was threaded on a needle and passed through the cheek about1 cm anterior to the papilla. That part of the cannula lying on the surface of the cheek was glued to tufts of wool, and penicillin cream was applied to the cheek wound. In two experiments the submaxillary duct was similarly cannulated with polythene tube of 1-0 mm diameter, 0 5 mm bore, passed between two incisor teeth and through the lower lip. All sheep were given11. of artificial saliva into the rumen after cannulation of the salivary ducts. The contents were removed from the reticulo-rumen on the morning of the experiment and the organ was washed clean with NaCl 0-9% (w/v); some experiments were performed on sheep with normally filled rumina. Contractions of,the reticulum and rumen were recorded on a kymograph with water parotid saliva was recorded with a Thorp drop-counter assembly. Recording. manometers at 6-12 cm water pressure; these were connected to air-filled balloons inserted into the sacs of the forestomach. Movements of the rumen were also observed directly. The flow of Submaxillary saliva was measured by timing its rate of flow along a graduated tube. Stimulation. Both tactile and stretch stimuli were applied to the forestomach and oesophagus. Tactile stimulation consisted of stroking the epithelium with a papillated rubber thimble; this was done very lightly so as to reduce compression and stretch to a minimum. Where the stimulated area was visible little or no distortion of the epithelium was seen. Stretch was applied by inserting tubes of known diameter into the cardia or reticulo-omasal orifice, or by the inflation of a balloon in the oesophagus, in the reticulum, in the various compartments of the rumen or against the reticulo-rumen fold. The tension produced varied considerably, especially during the contractions of the forestomach and the orifices; such stimuli also compressed the epithelium. Slight friction occurred when the animal moved, in spite of the balloons being held as still as possible. A mixed stimulus was applied deliberately on some occasions by gently squeezing the epithelium and musculature between finger and thumb. Experiments in which buffered solutions were introduced into the rumen were conducted on sheep fitted with two 2 cm diameter cannulae inserted into the dorsal rumen sac (Ash, 1959). Between testing the effects of different solutions the forestomach was thoroughly drained by suction and rinsed with NaCl 0-9 % (w/v). RESULTS Observations on the interior of the forestomach After emptying the forestomach of sheep fitted with large cannulae it possible to illuminate the interior of the rumen and observe its activity directly. With the exception of the left wall of the rumen and the most posterior parts of the dorsal and ventral blind sacs the whole of the interior of the rumen was visible (Fig. 1). When swallowing took place, the cardia, was

3 SENSITIVITY OF THE SHEEP FORESTOMACH 45 normally slit-like, opened and the smooth pink epithelium of the oesophagus could be seen. Food boli and swallowed saliva were ejected rapidly from the oesophagus into the rumen and immediately afterwards the lining of the terminal oesophagus was protruded and appeared briefly as a pink rosette. Localized muscular activity. Frequent contractions of small areas of the rumen wall could usually be seen in the region of the cardia; these were in addition to a more or less continuous pulsating movement of the cardia itself. Brief contractions of short lengths of the anterior and longitudinal pillars occurred in between the major contractions of the pillars; this activity increased during feeding. Throughout a feeding period the anterior pillar was usually in a state of partial contraction. On some occasions stimulation of the pillars caused an increase in local activity and the epithelium became flushed. Usually the reticulo-omasal orifice was tightly closed but it was possible to insert a finger through it. Tension round the finger increased with both phases of each of the reticulum contractions and during the contractions of the reticulo-rumen fold and of the anterior pillar. When a finger was passed along the omasal sulcus it was possible to feel the vela omasi and the smooth mucosa of the abomasum. Observations on rumination The introduction of the recording balloon into the reticulum and some of the manipulations made during the examination of the interior of the forestomach often caused rumination. When the fore-stomach contained digesta the sheep extended its head, a single contraction of the reticulum occurred and about the same time there was a contraction of the abdominal muscles and digesta were regurgitated. The regurgitated material could be seen passing up the oesophagus on the left side of the animal's neck and this was associated with an appreciable increase in parotid flow. A typical biphasic contraction of the reticulum followed 2-3 sec after the monophasic contraction associated with regurgitation. When a recording balloon was in the reticulum a further increase in parotid flow was often recorded during the declining phase of the biphasic reticulum contraction; without a recording balloon the second increase was slight or absent. Parotid secretion gradually declined during mastication of the bolus, to reach its lowest rate just before the bolus was swallowed. Variation in the strength of the contractions and in the duration of each phase was observed but the sequence of events was always the same. Stretching the reticulo-omasal orifice frequently caused a very powerful regurgitation. It appeared as if the regurgitated material was projected too far forward in the mouth, for instead of chewing the sheep shook the material from its mouth. In those sheep whose rumina had been emptied, attempted rumination occurred. As in the normal animal, the head was extended and a contraction

4 46 R. W. ASH AND R. N. B. KAY of the reticulum and abdominal muscles followed; usually a small amount of fluid was regurgitated. One or two chewing movements were made before swallowing. Again parotid secretion was slightly increased during regurgitation and during the declining phase of the biphasic reticulum contraction when a recording balloon was in the reticulum; without the balloon these effects were slight or wholly absent. In the empty preparation a series of monophasic contractions of the reticulum sometimes occurred at intervals of 5-20 sec, without each one being followed by a biphasic reticulum contraction. These were accompanied by other manifestations of attempted regurgitation. Toward the end of a period of rumination the time between each cycle and the next gradually increased. The interval between the last rumination cycle and the first biphasic reticulum contraction was always sec longer than the interval between succeeding biphasic contractions. A frequent observation was that sec before the onset of rumination the rate of parotid secretion began to increase. Mechanical stimulation of the oesophagus and forestomach The forestomach of the sheep is shown diagrammatically in Fig. 1. The incidence of rumination and the changes in parotid secretion and reticulum motility caused by local stimulation of the oesophagus and forestomach are summarized in Table 1. Oesophsgus ~~~~Dorsal sac Cardla ioesophaseal groove orul5 n Anzlrlor Longinudanal Postuaor \Retfieu\'I Fig. 1. Diagram of the reticulo-rumen of the sheep showing the position of structures referred to in the text. Parts of the forestomach and the thoracic oesophagus were very sensitive to mechanical stimulation. The sensitivity of the rumen was localized to specific structures. These were chiefly the cardia, the oesophageal groove, the reticulo-omasal orifice, the reticulum, the reticulo-rumen fold and the anterior and longitudinal pillars of the rumen. Stroking or rubbing a wide area of the

5 SENSITIVITY OF THE SHEEP FORESTOMACH 47 epithelium of the ventral or dorsal sacs of the rumen affected neither parotid secretion nor reticulum contractions. A gradient of decreasing sensitivity radiated caudally from the cardia and reticulum. Qualitatively different responses were obtained from different areas. For example, stretching the terminal 10 cm of the oesophagus or the cardiac orifice caused an appreciable increase in parotid flow but had variable effects on the reticulum and seldom caused rumination; the increased parotid flow TABLE 1. Region Oesophagus, lower 10cm Cardiac orifice Cardia and terminal oesophagus Reticulo-omasal orifice Reticulo-omasal orifice Walls of reticulum Reticulo-rumen fold and oesophageal groove Reticulo-rumen fold Anterior pillar of rumen Longitudinal pillar of rumen Posterior pillar of rumen Pillars and dorsal or ventral sacs or blind sacs of rumen Changes in parotid secretion and reticulum motility caused by mechanical stimulation of the forestomach No. of trials in which Parotid secretion increased* (max. rate of secretion in brackets Total no. Stimulus of trials ml./min) Stretch (condom (2-7) 1*5-2*0 cm diam.) Gentle stroking (2-5) Stretch (tube (2-7) 1*9-2-5 cm diam.) Gentle stroking Stretch ( cm) Gentle stroking Gentle stroking Stretch (balloon, ) Gentle stroking Gentle stroking Gentle stroking Stretch (balloon, ) 11 7 (1-5) (1-7) (1-5) (1-4) 7 7 (1-4) (1-5) 7 4 (1-3) 16 5 (1-3) 8 0 Frequency of reticulum contractions increased Rumination or attempted Frequency rumination of occurred reticulum during or contractions after the decreased stimulus a * When sheep were neither ruminating or being stimulated, parotid saliva flowed at rates of 0-2-2*3 ml./min. showed little or no adaptation during the application of the stimulus. On the other hand tactile stimulation of the anterior wall of the reticulum usually increased the frequency of the reticulum contractions but seldom caused any appreciable increase in parotid flow unless rumination occurred. These responses are shown in Figs. 2 and 3. Qualitatively different responses could also be obtained by the application of different stimuli to the same area. For example, stretching the reticulorumen fold or the reticulo-omasal orifice usualiy increased both the parotid

6 48 R. W. ASH AND R. N. B. KA Y Fig. 2. Stimulation of the anterior wall of the reticulum and cardia. Rumen empty. Records from above downwards: parotid saliva flow, reticulum, signal, time marker. a: Tactile stimulation of anterior wall of the reticulum; the three signals following this period of stimulation mark attempts at rumination. b: Tube 1F9 cm diameter inserted through cardia for a distance of 6 cm. Fig. 3. Tactile stimulation of the anterior wall of the reticulum. Rumen empty. Records from above downwards: reticulum, signal, time marker.

7 SENSITIVITY OF THE SHEEP FORESTOMACH 49 flow and the frequency of reticulum contractions; less often rumination was observed (Table 1). Tactile stimulation of these structures and the epithelium immediately around them amore frequently caused rumination and had a less pronounced effect on parotid secretion. Figures 4 and 5 show the responses to stimulation of the reticulo-omasal orifice and the reticulo-rumen fold. Examples of the responses that were obtained from tactile stimulation of the pillars of the rumen are shown in Fig. 6. Fig. 4. Stimulation of the reticulo-omasal orifice; rumen empty. Record from above downwards: parotid saliva flow, reticulum, signal, time marker. a: Tactile stimulation of rim of orifice, followed by two attempts at rumination. b: Tube 1-5 cm diameter inserted through orifice, followed by three attempts at rumination. The rumination that resulted from stimulation of the forestomach in the emptied preparation differed from rumination occurring spontaneously in normal sheep in that the intervals between regurgitation were reduced. Most of the stretch stimuli caused various signs of discomfort, such as grinding the teeth, arching of the back, agitated movements of the head, and occasionally stamping of the feet. Some stimuli that elicited this behaviour, such as distension of the compartments of the rumen, inhibited rumination, normal 4?HYSIO. CXLIX

8 50 R. W. ASH AND R. N. B. KA Y Fig. 5. Stimulation of reticulo-rumen fold; rumen empty. Records from above downwards: parotid saliva flow, reticulum, signal, time marker. a: Tactile stimulation; attempts at rumination began after 1 min and continued after stimulation stopped. b: Stretch of reticulorumen fold by inflation of a balloon over the fold to 500 ml. Rumination was inhibited immediately and started again 2-5 min after the end of stimulation. Fig. 6. Tactile stimulation of the pillars of the rumen; rumen empty. Records from above downwards: parotid saliva flow, reticulum, signal, time marker. a: Right longitudinal pillar; attempts at rumination began after 45 sec. b: Free edge of posterior pillar. c: Free edge of anterior pillar; attempts at rumination began after 90 sec. The correlation between parotid flow and reticulum contractions (see text) can be seen toward the end of the record.

9 SENSITIVITY OF THE SHEEP FORESTOMACH 51 reticulum contractions and parotid secretion (Fig. 7) but others, such as stretching the oesophagus, the cardia, the reticulo-omasal orifice or the reticulorumen fold, were always excitatory to the parotid gland and occasionally to the reticulum. Squeezing the epithelium and musculature of the anterior pillar and twisting the rumen cannula were usually inhibitory to both the parotid gland and the reticulum; alternatively, gentle squeezing of musculature of the reticulum caused a response similar to that produced by tactile stimulation. Fig. 7. The inhibitory effect of inflating balloons in the rumen; rumen empty. Records from above downwards: parotid saliva flow, reticulum, signal, time marker; the two records were taken on different days from the same sheep. a: Inflation of a balloon (2000 ml.) in the posterior ventral blind sac; rumination was inhibited immediately and began 2-5 min after the balloon was deflated. b: Inflation of a balloon in the dorsal blind sac to 1100 ml.; rumination was inhibited immediately and did not restart. The flow of submaxillary saliva was recorded in two experiments. Submaxillary secretion was affected relatively little by rumination or by stimulation of the forestomach, although distension of the cardia and oesophagus caused a moderate response (Table 2). Some of the responses studied varied quantitatively and qualitatively both between sheep and in the same sheep on different days. Tactile stimulation of the anterior pillar usually caused prolonged rumination but in one sheep this stimulation caused little or no rumination and occasionally inhibition. Towards the end of an experiment lasting about 6 hr all the sheep showed 4-2

10 52 R. W. ASH AND R. N. B. KAY diminished or even inhibitory responses to most tactile stimuli. However, stretching the oesophagus, the cardia, the reticulo-omaaal orifice or the reticulo-rumen fold invariably caused a powerful parotid salivary response. It was unlikely that the variability observed between sheep or between experiments on the same sheep was due to the administration of anaesthetic the previous day. In one experiment pentobarbitone 3-6 mg/kg was injected intravenously and this caused the sheep to become drowsy and unsteady on its feet. Tactile stimulation of the anterior pillar still caused rumination, although the frequency of both normal diphasic and rumination cycles was decreased. TABLE 2. Responses of the submaxillary and parotid glands to various stimuli in two sheep Rate of flow (ml./min) Sheep no. 3 Sheep no. 6 Stimulus Submaxillary Parotid Submaxillary Parotid None * Tactile, anterior wall of reticulum Stretch, reticulo omasal orifice 1-5 cm Stretch, cardia 1-9 cm Eating chopped hay *5 or dried grass Local anaesthesia of the forestomach When ml. of amethocaine HC 1 % (w/v) was injected into the terminal oesophagus or into the lumen of the reticulum the contractions of the reticulum stopped, although regular contractions of the rumen continued (Fig. 8). It appeared that the anaesthetic was affecting the receptors of the reticulum or cardia or the sensory nerves leaving these regions, for in further experiments the parotid response to stimulation of the cardia was greatly reduced. Efferent nerves to the parotid gland were unaffected, for a normal parotid response to feeding was obtained. In addition, the motor fibres to the reticulum or the reticulum muscle itself were also blocked by the anaesthetic, for stimulation of the thoracic vagus nerves with chronically implanted electrodes failed to cause the reticulum to contract, although the normal rumen contraction was elicited. The contractions of the rumen which persisted after anaesthetizing the reticulum were more regular than those which Phillipson (1939) found when the reticulum was inhibited by distending the abomasum. Clearly neither contractions of the muscle of the reticulum, nor the afferent vagal impulses which accompany such contractions (Iggo, 1956), are necessary for the occurrence of cyclic activity of the rumen.

11 SENSITIVITY OF THE SHEEP FORESTOMACH 53 Fig. 8. The effect of injecting amethocaine HC1 15 ml. 1% (w/v) into the lumen of the reticulum; rumen empty. Records from above downwards: reticulum, dorsal blind sac of the rumen, signal, time marker. The largest excursions of the rumen record were caused by contractions of the dorsal blind sac alone and their frequency was irregular; the smaller excursions were caused by contractions of the whole of the dorsal sac (including the blind sac) and these were followed in some cases by still smaller contractions of the ventral sac; the contractions of the whole of the dorsal sac occurred regularly and at the same frequency as the reticulum contractions. Stimulation of the forestomach with fatty acids The introduction into the rumen of fatty acid solutions at ph 3-6-5*0 inhibits the contractions of the forestomach in conscious sheep (Ash, 1959), and at rather lower ph values causes a transient increase in parotid secretion in decerebrate sheep (Kay, 1958). In seven further experiments on conscious sheep both parotid secretion and reticulum contractions were recorded. Two to four litres of fatty acid solutions at 370 C were introduced into the rumen. The solutions tested were 50, 100, 167 and 200 mm acetate, 20, 50 and 150 mm butyrate, 143 mm acetate+ 57 mm butyrate, and 25 mm acetate+ 15 mm propionate + 10 mm butyrate. The 20, 50 and 100 mm solutions were made approximately isotonic by the addition of NaCl. When buffered at ph none of the solutions had a greater excitatory or inhibitory effect on the reticulum or parotid gland than the same volume of 0-9 % NaCl solution except for the 150 mm butyrate solution, which inhibited the reticulum for 10 min. When buffered at ph all these solutions with the exception of the 20 mm butyrate and the 50 mm acetate either totally inhibited the reticulum contractions or greatly reduced their amplitude. The inhibition lasted min in the case of the 50 mm solution or until the solution was removed

12 54 R. W. ASH AND R. N. B. KAY min later in the case of the stronger solution. Parotid secretion increased with all the solutions at ph The increase in flow began sec after starting to pour the solution into the rumen and the response ceased after 2-15 min. The rate of secretion at the peak of the response was 2-6 times greater than the initial flow. These responses are shown in Fig. 9. The volume of the additional parotid saliva secreted by one gland as a result of pouring acid solution into the rumen was 1-18 ml. Fig. 9. The effect of introducing into the empty rumen 41. of fatty acid buffer (mm): acetate 25, propionate 15, butyrate 10, ph 3*7. Records from above downwards: parotid saliva flow, reticulum, signal, time marker. Four samples were drawn from the rumen at the signals S and had ph values of 3 9, 4.0, 4-1 and 4-2 respectively. DISCUSSION The areas of the forestomach sensitive to mechanical stimulation correspond to those areas in which Hill (1957, 1958) was able to demonstrate nervous structures that stain with methylene blue and which penetrate into the epithelium. A striking feature of the present experiments was the ease with which tactile stimulation, and apparently in some cases stretch, of certain parts of the forestomach caused rumination. In spite of the diverse opinions expressed on the factors causing rumination under normal feeding conditions

13 SENSITIVITY OF THE SHEEP FORESTOMACH 55 the experiments reported in this paper suggest that mechanical stimuli to the reticulo-rumen may well be an important factor. Neither intravenous injections of short-chain fatty acids (Le Bars, Lebrument, Nitescu & Simonnet, 1954; R. W. Ash, unpublished observations) nor the introduction of fatty acid buffers into the rumen in various concentrations and over a wide range of ph values cause rumination. The application of fatty acid and of NaCI 09 % (w/v) to localized areas of the forestomach did cause rumination in a few experiments, but in these instances the rumination may well have been due to mechanical stimulation involved in the application of the chemicals (Ash, 1959). Rumination may reduce the coarseness of the rumen digesta by chewing and increase the fluid content by the increased flow of saliva. It is reasonable to suggest that reflex mechanisms exist that relate rumination to the physical properties of the forestomach contents. The time sheep spend ruminating each day appears to be related to the roughness of the rumen contents. Gordon (1958) found that sheep fed on chopped hay spent an hour longer ruminating than sheep fed on long hay, and finely grinding the hay nearly halved the rumination time. Moreover, there is a tendency for the coarser hay and corn-husk particles to form a layer on top of the more fluid portion of the rumen contents. The contents of the ventral sac normally include somewhat less solid matter, while those of the reticulum are fluid in nature. The coarser particles are thus well placed to stimulate the anterior pillar and sensitive areas of the dorsal sac provided that the 'fluid level' is at a suitable height. However, more experimental evidence is required to assess the full significance of reflex excitation from the forestomach in the initiation of rumination. Rumination is similar in sheep whether the rumen is full or has been artificially emptied. The main differences in the sheep with an empty rumen were the much shorter chewing period, the more frequent occurrence of the cycles and on some occasions repeated attempts at regurgitation. The increased parotid secretion which accompanied attempted rumination in the sheep with empty rumina may perhaps be the result of stimulation of receptors as a result of increased forestomach motility. In normal rumination salivary flow will be reinforced by the oesophageal distension and buccal stimulation associated with regurgitation and chewing. Stretch stimuli which caused symptoms of discomfort were not necessarily inhibitory either to the reticulum or to the parotid gland. Payne & Poulton (1927) found that distension of the human oesophagus caused painful sensations and these became worse during contractions which were unable to overcome the stretch. Similarly in our experiments discomfort seemed to increase during contractions of the oesophagus or of structures in the forestomach when these were stretched. Fatty acid solutions buffered at about ph 4 0 have been shown to inhibit

14 56 R. W. ASH AND R. N. B. KAY reticulo-rumen contractions by a peripheral mechanism (Ash, 1959). In the present experiments such buffers also had a transient stimulatory effect on parotid secretion as was found in decerebrate sheep (Kay, 1958). The ph required to elicit this response is well below the range found in normal rumen contents and the extra saliva secreted is not sufficient to elevate the ph of the rumen contents by more than a small amount. SUMMARY 1. Mechanical and chemical stimuli were applied through a large-diameter cannula to the reticulo-rumen and oesophagus of conscious sheep. Reticulum contractions and parotid secretion were recorded simultaneously. 2. Stretching the terminal oesophagus, cardia, reticulo-rumen fold or reticulo-omasal orifice caused large increases in parotid secretion. Light tactile stimulation of these areas and of the walls of the reticulum and the anterior pillar had a small effect on parotid flow but frequently accelerated reticulum contractions and caused rumination. Distension of the rumen sacs with a balloon inhibited both motility and saliva flow. 3. Similar responses to mechanical stimulation were obtained irrespective of whether the reticulo-rumen contained digesta or had been emptied. 4. The application of a 1-2% solution of amethocaine HCI to the reticulum abolished the regular contractions of the organ and the contractions caused by vagal stimulation. The rumen continued to contract regularly. 5. The introduction of fatty acid solutions buffered at ph 3 7-4O0 inhibited reticulo-rumen contractions and caused a transient increase in parotid secretion. 6. The role of stimuli acting in the reticulo-rumen on normal rumination behaviour is discussed. We wish to thank Mr J. Dunnet for technical assistance. REFERENCES ASH, R. W. (1957). A large-diameter rumen cannula for sheep. J. Physiol. 139, 6P. ASH, R. W. (1959). Inhibition and excitation of reticulo-rumen contractions following the intro. duction of acids into the rumen and abomasum. J. Physiol. 147, ASH, R. W. & KAY, R. N. B. (1957). The responses of the reticulum and parotid gland of the conscious sheep to stimulation of the forestomach. J. Physiol. 139, 23-24P. BELL, F. R. (1958). The electroencephalogram of conscious goats and its association with the ruminant state. J. Physiol. 14,3, 46-47P. CTL&Ax, R. & WEIss, K. E. (1952). Reflex salivation in sheep and goats initiated by mechanical stimulation of the cardiac area of the forestomach. J. S. Afr. Vet. med. As8. 23, COMLINE, R. S. & KAY, R. N. B. (1955). Reflex secretion by the parotid gland of the sheep. J. Physiol. 129, 55-56P. COMLINE, R. S. & TITCHEN, D. A. (1957). Reflex contractions of the reticulum and rumen and parotid salivary secretion. J. Physiol. 139, 24-25P. DOwNIE, H. G. (1954). Photokymographic studies of regurgitation and related phenomena in theruminant. Amer. J. Vet. Res. 15,

15 SENSITIVITY OF THE SHEEP FORESTOMACH 57 DZIUK, H. E. & SELLERS, A. F. (1955). Physiological studies of the vagal nerve supply to the bovine stomach. 1. Comparison of responses in milk-fed and roughage-fed calves using a chronic intrathoracic vagal electrode technique. Amer. J. Vet. Res. 16, GORDON, J. G. (1958). The act of rumination J. agric. Sci. 50, HrLL, K. J. (1957). Nervous structures in the reticulo-rumen epithelium of the goat. J. Physiol. 139, 4-5P. HILL, K. J. (1958). Nervous structures in the reticulo-rumen epithelium of the lamb. J. Physiol. 143, P. IGGO, A. (1956). Central nervous control of gastric movements in sheep and goats. J. Physiol. 131, KAY, R. N. B. (1958). Continuous and reflex secretion by the parotid gland in ruminants. J. Physiol. 144, KAY, R. N. B. & PHILLIPSON, A. T. (1957). Salivary secretion of anaesthetized sheep during distension of the rumen and eosophagus. J. Physiol. 139, 7P. LE BARs, H., LEBRUMENT, J., NITESCU, R. & SIMONNET, H. (1954). Recherches Sur la motricite du rumen chez les petits ruminants. Action de l'injection intraveineuse d'acides gras a courte chaine. Bull. Acad. vit. Fr. 27, PAYNE, W. W. & POULTON, E. P. (1927). Experiments on visceral sensation. Part I. The relation of pain to activity in the human oesophagus. J. Physiol. 63, PHILLIPSON, A. T. (1939). The movements of the pouches of the stomach of the sheep. Quart. J. exp. Physiol. 29, SCHALK, A. F. & AMADON, R. S. (1928). Physiology of the ruminant stomach (bovine). Study of the dynamic factors. North Dakota Agric. Exper. Sta. Bull. 216, TITCHEN, D. A. (1958). Reflex stimulation and inhibition of reticulum contractions in the rumi. nant stomach. J. Physiol. 141, 1-21.