(Colin, 1886; Scheunert & Trautmann, 1921; Scheunert, Krzywanek & Zimmermann, 1929; Denton, 1957 a, b). The rate of secretion is reduced but is

Transcription

1 463 J. Physiol. (I958) I44, CONTINUOUS AND REFLEX SECRETION BY THE PAROTID GLAND IN RUMINANTS By R. N. B. KAY* From the Physiological Laboratory, University of Cambridge (Received 6 June 1958) The parotid glands of adult ruminants secrete saliva rapidly and continuously. The large volume of alkaline saliva produced helps to maintain the relatively constant ph and the fluid nature of the fermenting contents of the rumen. The rate of secretion varies; it increases particularly, during feeding and rumination (Colin, 1886; Scheunert & Trautmann, 1921; Scheunert, Krzywanek & Zimmermann, 1929; Denton, 1957 a, b). The rate of secretion is reduced but is not annulled by acute or chronic denervation of the gland (Eckhard, 1867, 1893; Krinitsin, 1940; Coats, Denton, Goding & Wright, 1956), nor by the injection of atropine (Babichev, Perstnov & Kulesco, 1930; Coats et al. 1956). Clark & Weiss (1952) were able to stimulate parotid secretion in anaesthetized sheep by brushing either the oesophagus or the cardiac region of the rumen; the sensory fibres concerned coursed in the cervical vagus nerves. On the other hand Coats et al. (1956) found that although chemical, electrical or mechanical stimulation of the mouths of sheep sometimes increased the rate of parotid secretion, such stimuli were ineffective when applied to the rumen. The experiments described in this paper confirm and extend earlier work on the secretion of parotid saliva in sheep and define some of the reflex mechanisms which influence the rate of secretion. Observations were also made on the submaxillary glands of sheep and on the parotid glands of goats and calves. A preliminary account of some of these results has been given (Comline & Kay, 1955). METHODS Preparations. Nineteen experiments were undertaken on Welsh Mountain sheep 6-15 months of age. These were decerebrated in the manner described by Comline & Titchen (1951). After fasting for hr. anaesthesia was induced with ethyl chloride and maintained with ether; the brain stem was transected in a plane passing through the anterior colliculi and the mammillary bodies, and anaesthesia was then discontinued. * Present address: Rowett Research Institute, Bucksburn, Aberdeenshire.

2 464 R. N. B. KA Y Other experiments were conducted on adult sheep and goats and on Jersey calves under chloralose anaesthesia. Chloralose (40-50 mg/kg body weight) was injected through a cannula nserted into the femoral vein after anaesthesia had been induced with ethyl chloride and maintained with ether. Nerve stimulation. Perspex-shielded bipolar platinum electrodes were used for the stimulation of nerve trunks. The stimuli were delivered from a Palmer induction coil giving about 70 pairs of impulses per second, or from a neon tube stimulator. In ruminants the secretory nerve to the parotid gland is derived from the buccal branch of the mandibular nerve and forms filaments which join the parotid duct on the surface of the masseter muscle and course beside the duct into the gland (Moussu, 1890). This nerve was called the parotid nerve by Moussu and will be referred to as such in this paper; it has also been called Moussu's nerve (Coats et al. 1956). The parotid nerve was isolated and stimulated either below the masseter muscle, together with the buccal nerve, or in its course beside the parotid duct. Intracranial stimulation of nerves was carried out after removal of the medulla and mid-brain from preparations which had previously been decerebrated. After thoracotomy, the oesophageal branches of the vagus nerves were isolated and stimulated cm anterior to the diaphragm; such sheep were ventilated with a 5% CO2 + 95% 02 gas mixture from a positive pressure pump. Records. One or both parotid ducts were cannulated on the surface of the masseter muscle, care being taken to avoid damage to the parotid nerve. The rate of delivery of drops of saliva was recorded with a Thorp impulse counter. The volume of the drops varied with their rate of formation. For example, in one case in which the electrodes of the drop counter tube were 4 mm apart, it was found that the average volume of a drop of parotid saliva was ml. at a flow of 1 ml./min, ml. at 5 ml./min, and 0*064 ml. at 10 ml./min; the corresponding figures for the volumes of drops of blood were 0-046, 0 049, and ml. In most experiments the rate of secretion did not exceed 5 ml./min. Blood pressure was recorded from the femoral artery. At the end of most experiments the parotid glands were excised, freed from lymph glands and weighed. Injections. Injections into the common carotid artery were made through fine polythene tubing inserted centrally via a thyroid or pharyngeal artery, and intravenous injections were given into a cannulated femoral vein. All doses are given as amount of drug per kilogram body weight. Acetylcholine chloride (Roche Products Ltd), atropine sulphate (British Drug Houses), Diamox (acetazolamide, 2-acetamido-1,3,4-thiadiazole-5-sulphonamide; Lederle), heparin (Roche Produots Ltd), hexamethonium bromide (May & Baker) and pilocarpine nitrate (British Drug Houses) were each dissolved in 0-9% NaCl solution. Rogitine (phentolamine; Ciba) was injected as the solution supplied by the manufacturers. RESULTS Secretion of the denervated sheep parotid gland A continuous secretion of parotid saliva was observed in all experiments. Section of the parotid nerve did not alter the rate of secretion in the majority of anaesthetized preparations, although in many decerebrate preparations the flow was somewhat diminished. The rate of secretion of a denervated parotid gland was generally between 0-5 and 1-6 ml./g parotid tissue/hr. Isolation of the denervated parotid gland from all connexions with the preparation except the carotid artery and jugular vein did not further reduce its rate of secretion. In four cases such isolated glands were excised and perfused with blood from a heart-lung preparation of the sheep. These glands

3 PAROTID SECRETION IN RUMINANTS 465 continued to secrete until the heart-lung system failed 1-4 hr later, but generally at a lower rate. In addition, the composition of the saliva changed at the onset of perfusion in that the concentrations of sodium and bicarbonate fell and those of potassium and chloride rose. The blood flow through the perfused glands was unusually high. The intravenous injection of drugs blocking nervous transmission was no more effective in reducing parotid secretion than denervation of the gland. The injection of atropine sulphate 1 mg/kg or of hexamethonium bromide 2 mg/kg, which wholly extinguished reflex excitation of the parotid, did not reduce the rate of secretion of the denervated gland. Even as much atropine sulphate as 10 mg/kg was without effect. Injection of the adrenergic blocking agent Rogitine 1 mg/kg, which was sufficient to annul the effects on the parotid of stimulation of the peripheral end of the cervical sympathetic nerve (Kay, 1958b), did not influence the rate of secretion. In addition it was found that the injection of the carbonic anhydrase inhibitor Diamox 30 or 40 mg/kg into two anaesthetized sheep that had not been deprived of food did not affect either the rate of flow or the composition of the parotid saliva, although it caused a marked increase in urinary bicarbonate and base. 1 mih IX Vll Cut par-otid l+ix VII nei ve Fig. 1. Spinal sheep. The effects of intracranial stimulation of the peripheral ends of the glosso. pharyngeal (IX) and facial (VII) nerves on parotid secretion (induction coil, 12 cm). The responses disappeared after section of the parotid nerve. Records from above downwards: parotid saliva flow (drop counter returned to base line at 30 sec intervals); signal; time marker, 1 min. Secretory innervation of the sheep parotid gland Intracranial stimulation of the peripheral ends of cranial nerves gave similar results in three preparations. The rate of parotid secretion was increased by stimulation of the glossopharyngeal nerve and to a less extent by stimulation of the facial nerve (Fig. 1). Section of the parotid nerve or the injection of hexamethonium bromide abolished these responses. Stimulation of the peripheral ends of the trigeminal, vagus, accessory and hypoglossal nerves did not increase the rate of secretion. Stimulation of the peripheral end of the buccal branch of the mandibular nerve produced a copious secretion of parotid saliva. This response was not reduced by injection of hexamethonium bromide 2 mg/kg which annulled the

4 466 R. N. B. KAY 466 R.B A reflex excitation of the opposite gland. It appeared, therefore, that the parotid secretory filaments that course in the buccal nerve consist of post-ganglionic fibres. Histological examination supported this view; bundles of fine unmyelinated fibres were found within the buccal nerve, and such fibres formed the filaments that ran beside the parotid duct and its tributaries. In some experiments the parotid was dissected out until the jugular vein carried only the venous blood flowing from the gland. After the injection of heparin this venous effluent was diverted through a cannula tied into the central end of the facial vein and recorded with a drop counter. Fig. 2 shows the effects of stimulating the peripheral end of the buccal nerve in such a Par-otid blood CL Parlotid -e 13O0 1 oojn i Fig. 2. Sheep; chloralose anaesthesia. The effects of stimulation of the peripheral end of the parotid nerve on the flow of parotid blood and parotid saliva (induction coil, 9 5 cm). Records from above downwards: parotid venous blood flow (drop counter returned to base line at 5 sec intervals); parotid saliva flow (drop counter returned to base line at 30 sec intervals); blood pressure; signal; time marker, 1 min. preparation. It may be seen that the parotid blood flow was increased markedly and that the relative increase in salivary secretion was even greater. Reflex stimulation of the gland had similar effects. Fig. 3 demonstrates that the intravenous injection of atropine sulphate 20,g/kg caused a marked and equal reduction in both the secretion of saliva and the vasodilation produced either by stimulation of the buccal nerve or by the intracarotid injection of 10,ug of acetylcholine chloride. The responses were completely annulled 30 sec after a further injection of atropine sulphate 100,ug/kg. Reflex stimulation of parotid secretion in sheep Stimulation of the mouth. In decerebrate preparations either mechanical or chemical stimulation of the mouth increased the flow of parotid saliva. Rubbing a brush between the molar teeth and the tongue was the most

5 PAROTID SECRETION IN RUMINANTS 467 effective stimulus (Fig. 4). The secretory response of the ipsilateral gland was much greater than that of the contralateral gland. Other areas of the mouth were usually much less sensitive in this respect; for instance, brushing between the molar teeth and the cheek (Fig. 4), or between the incisors, dental pad and Parotid blood Parotid saliva I 100-1, 50-1 min.-m lopg Bluccal 10,g Buccal 10/3g Buccal ACh nerve ACh nerve ACh nerve 20fug/kg 1 OOpug/kg Atropine Atropine sulphate sulphate Fig. 3. Sheep; chloralose anaesthesia. The I.v. injection of atropine abolished both the secretory and the vascular responses of the parotid gland to the injection of 10,ug of acetylcholine chloride (ACh) into the ipsilateral carotid artery and to stimulation of the peripheral end of the buccal nerve (induction coil, 8 cm). Records from above downwards: parotid venous blood flow (drop counter returned to base line at 5 sec intervals), parotid saliva flow (drop counter returned to base line at 30 sec intervals); blood pressure; signal; time marker, 1 min. L. parotid R. parotid i1 1 COi E miin, ) u Fig. 4. Decerebrate sheep. Stimulation of the buccal epithelium. Records from above downwards: left and right parotid saliva flow (drop counters returned to base line at 1 min intervals); blood pressure; signal; time marker, 1 min. Rubbing a test-tube brush between the tongue and molar teeth, on the left (a) and right (b) sides increased parotid secretion, especially ipsilaterally, but brushing similarly between the cheeks and molar teeth on the left (c) and right (d) sides had no effect.

6 468 R. N. B. KAY lips, had little or no influence on parotid secretion. The introduction of 20 ml. of 0 5 M acetic acid into the mouth increased the flow of parotid saliva in some experiments but not in all; the same volume of tap water, of 0.5 M-NaCl, or of 041 N-HCI produced no response. The reflex secretion caused by mechanical or chemical stimulation of the mouth was abolished by cutting both the lingual and glossopharyngeal nerves or the parotid nerve, or by the intravenous injection of atropine. Stimulation of the central end of the lingual nerve usually caused a two- to threefold increase in parotid secretion. The effect of stimulation of the glossopharyngeal nerve was less regular. The oesophagus. In two preparations the oesophagus was transected and cannulated in the neck, and the upper and lower parts were stimulated with a bottle brush. Stimulation of the upper cervical oesophagus had little influence on parotid secretion but the flow of saliva was doubled by the introduction of the brush into the thoracic oesophagus. A much greater response was produced by distension of the lower half of the thoracic oesophagus and the abdominal oesophagus with a rubber tube 2-5 cm in diameter. When the tube was held in a position without movement the flow of saliva diminished slowly over a period of minutes; gentle movements of the tube rapidly restored the flow to its former high rate. The rumen and reticulum. In twelve decerebrate or anaesthetized preparations the dorsal sac of the rumen was incised and the contents were removed to allow manual stimulation of the epithelium of the forestomach. Light stroking of the cardiac orifice was the most effective stimulus to parotid secretion. The initial rate of parotid secretion in a decerebrate preparation, after its rumen had been emptied, is shown in Fig. 5 a. A hand was then placed in the anterior dorsal sac of the rumen, increasing the salivary flow by about three times (Fig. 5b, first minute). The mucosa of the anterior dorsal sac was slightly stretched and was gently rubbed against the hand by respiratory movements. Light stroking of the cardia with a finger-tip then caused a further doubling of parotid secretion after a delay of about 5 sec. All these responses were annulled by injection of atropine (Fig. 5c). Responses that were almost as great as those elicited by stroking the cardia were obtained by light stroking of the reticulo-omasal orifice or by stretching this orifice or the cardia with a finger. Stroking the lips of the oesophageal groove, the reticulo-rumen fold or the epithelium of the reticulum gave rather smaller responses. Light sustained digital pressure on these regions was a much less effective stimulus than touch or stretch. Parotid secretion was not increased by mechanical stimulation of the walls of the ventral sac or of the posterior part of the dorsal sac of the rumen. Parotid secretion was also increased in four decerebrate preparations by the introduction into the empty washed rumen of 100 ml. of each of the following

7 PAROTID SECRETION IN RUMINANTS 469 acids: 0.5 M-solutions of acetic acid, propionic acid, n- or iso-butyric acid, lactic acid or 01 N-HCI. Similar responses were obtained with each of these acids. The responses began after a delay of about 1 min and lasted for about 5 min; the peak rate of secretion was two to four times greater than the resting flow. The introduction of 100 ml. of tap water, 0-9 % NaCl, 1-15% KCI, or 0 5 M sodium acetate produced no response. L. parotid R. pat-otid_d co TO 80- sec._ Stroke cardia Stroke cardia Atropine Fig. 5. Decerebrate sheep. Parotid secretion in response to stimulation of the cardia. Records from above downwards: left and right parotid saliva flow (drop counters returned to base line at 1 min intervals in a, and at 30 sec intervals in b and c); blood pressure; signal; time marker, 10 sec. a, Rumen empty; b, hand in rumen; cardia stroked with a finger-tip; c, cardia stroked with a finger-tip, and the response annulled by the i.v. injection of atropine sulphate 0 5 mg/kg. The reflex secretion by the parotid gland during mechanical stimulation of structures in the stomach was completely abolished by section of either the thoracic or the cervical vagus nerves. In the thorax the distribution of the sensory fibres concerned between the dorsal and the ventral oesophageal branches of the vagus nerves appeared to be variable. These nerves were cut cm anterior to the diaphragm and their central ends stimulated in five preparations. In one, stimulation of the central end of the dorsal branch caused a tenfold increase in parotid secretion after a delay of about 5 sec (Fig. 6); stimulation of the ventral branch had no effect. In the remaining four preparations parotid responses could be obtained from either branch, but only in one preparation was a response obtained from the ventral branch as great as that obtained from the dorsal. After section of one cervical vagus nerve, the reflex response of the ipsilateral parotid gland to mechanical stimulation of the forestomach was much reduced; that of the contralateral gland was only lessened to a slight extent. Similarly, stimulation of the central end of one cervical vagus caused the ipsilateral parotid to secrete much more rapidly than the contralateral gland. 30 PHYSIO. CXLIV

8 470 R. N. B. KAY E c sec Dorsal vagus Ventral vagus Fig. 6. Decerebrate sheep. Stimulation of the branches of the thoracic vagus nerve (induction coil, 13 cm). Records from above downwards: parotid saliva flow (drop counter returned to base line at 30 sec intervals); blood pressure; signal; time marker, 30 sec. a, stimulation of the dorsal oesophageal vagus; b, stimulation of the ventral oesophageal vagus. The submaxillary gland of the sheep This gland was found to be innervated by a branch of the lingual nerve which enters the gland with the submaxillary duct; this arrangement is similar to that found in other species. In most anaesthetized preparations a very slow continuous flow of submaxillary saliva occurred but this did not exceed a rate of 0.01 ml./g submaxillary tissue/hr. In decerebrate preparations stimulation of the forestomach caused little or no secretion. In one preparation stimulation of the central end of the cervical'vagus nerve produced a flow of saliva from the ipsilateral submaxillary gland of 0 15 ml./g submaxillary tissue/hr; this was less than one tenth of the flow elicited by stimulation of the central end of the ipsilateral lingual nerve. The parotid glands of goats and calves No differences were found between the innervation and responses of the parotid glands of goats and those described for sheep. The continuous secretion of the denervated gland was observed and reflex secretion was caused by mechanical stimulation of the sensitive regions of the mouth, oesophagus and forestomach. The innervation of the parotid gland of the calf was also similar to that described in the sheep. In calves less than 1 month old there was no continuous secretion of parotid saliva and stimulation of the peripheral end of the cut parotid nerve or the intravenous injection of pilocarpine elicited little response from the gland. By the age of 3 months the continuous parotid secretion was apparent and persisted after denervation of the gland and a copious flow of saliva was caused by stimulation of the parotid nerve. In these older calves, light stroking of the cardia, the oesophageal groove or the walls of the reticulum produced a rapid reflex secretion of parotid saliva. The responses were abolished by section of the parotid nerve or by injection of atropine.

9 PAROTID SECRETION IN RUMINANTS 471 DISCUSSION The secretion of the denervated parotid gland. It was shown by Eckhard (1867, 1893) and confirmed by Krinitsin (1940) and by Coats et al. (1956) that the parotid gland of the sheep continues to secrete following denervation. The experiments reported in this paper give further support to this observation. In addition to its resistance to atropine (Babichev et al. 1930; Coats et al. 1956) the secretion of the denervated gland is unaffected by the injection of hexamethonium, of the adrenergic blocking agent Rogitine and of the carbonic anhydrase inhibitor Diamox. It differs from the 'paralytic' secretion of the denervated submaxillary gland (Bernard, 1864) in that it is fully present from the time of denervation and not only after the lapse of several days, during which time the submaxillary gland becomes supersensitive to excitatory agents (Emmelin, 1952). Atropine-insensitive secretion by denervated salivary glands is not unknown, for it has been carefully studied by Emmelin (1953) in excised sublingual glands of the cat. Krinitsin (1940) found that the secretion of the denervated ruminant parotid progressively diminishes during prolonged starvation and suggested that this secretion is not due to some property of the gland itself, as claimed by Eckhard (1893), but is stimulated by absorbed products of digestion. Such a theory does not explain the secretion of the isolated and perfused parotid gland, first demonstrated by Coats et al. (1956), and further experiments are required to establish the cause of this secretion. It is unlikely that the continuous secretion contributes more than a small fraction of the total volume of parotid secretion. In twenty-three of the sheep used in the present experiments, whose average weight was 34 kg, the average weight of a single parotid gland was 13 g. The resting secretion of a 13 g parotid, assuming a rate of ml./g parotid tissue/hr, would amount to about ml. of saliva/24 hr, whereas in conscious sheep a single parotid is reported to secrete saliva/24 hr (Denton, 1957 b). Two aspects of the flow of blood through the sheep's parotid gland deserve attention. The first is that stimulation of the buccal nerve does not increase the parotid blood flow to as great an extent as the rate of secretion of saliva. This suggests that at rapid rates of secretion there may be a relative reduction in the amount of plasma electrolytes that are available for the formation of a given volume of saliva. This factor may contribute to the depression of the concentrations of potassium and phosphate in the saliva that is observed as the rate of secretion is increased (Coats & Wright, 1957). The second point is that the nervously excited secretion and the attendant vasodilation in the sheep's parotid are equally and delicately sensitive to blockage by atropine. In the submaxillary gland it has long been known that glandular vasodilation is much less sensitive to atropine than is salivary secretion (Heidenhain, 1872). 30-2

10 472 R. N. B. KA Y No explanation can be offered for the different reaction of the sheep's parotid gland. Reflex secretion. The present experiments have defined many of the reflex arcs controlling parotid secretion. In all cases the efferent limb consists of preganglionic fibres that leave the brain with the facial and glossopharyngeal nerves and of post-ganglionic fibres that initially course with the buccal nerve and subsequently reach the gland as filaments that accompany the parotid duct. The position of the synapses between these fibres has not been studied, but it is probably in the otic ganglion, as in other species (Shute, 1956). The afferent limbs of the reflex arcs have been established as fibres from the stomach which course in the vagus nerves and as fibres from the mouth distributed between the facial and glossopharyngeal nerves. The methods employed in the present experiments do not permit an exact definition of the nature of the stimuli to which the receptors concerned in parotid secretion respond. Striking responses were associated with brushing or light stroking of certain regions of the mouth and of the cardia, the reticulo-omasal orifice, the lips of the oesophageal groove, the reticulo-rumen fold and nearby regions. Such stimuli were presumably largely tactile in nature, but undoubtedly the stroking would have dragged on the epithelium and compressed the musculature to a small extent. In addition, stretch of the terminal oesophagus, cardia and reticulo-omasal orifice proved little less effective, and in this form of stimulation stretch and compression of the epithelium and musculature would have predominated. Stretch of the reticulo-rumen fold (Comline & Titchen, 1957) and distension of the oesophagus with gas (Kay & Phillipson, 1957) have also been found to increase greatly the flow of parotid saliva in decerebrate or anaesthetized sheep. In decerebrate preparations of sheep, goats and calves Titchen (1958) was able to initiate or augment contractions of the reticulum by stretch of the reticulum, omasal canal and abomasum and by tactile stimulation of the lower thoracic oesophagus and abomasum. Ash & Kay (1957) found that in conscious sheep stretch or tactile stimulation of the lower thoracic oesophagus, cardia and reticulo-omasal orifice both excited parotid secretion and had variable effects on reticulum motility. The evidence suggests that both stretch and tactile receptors occur in the ruminant forestomach and that each group of receptors may influence both parotid secretion and reticulum motility. The stretch receptors concerned may be similar to those studied in the goat by Iggo (1955) who recorded afferent volleys in the vagus nerve from tension receptors in the reticulum. Nervous structures that may account for the sensitivity to touch are those found by Hill (1957) in the subepithelial connective tissue of the forestomach of the goat; fibrils from these structures penetrate into the keratinized layer of the epithelium. The reflex parotid secretion caused by stimulation of the buccal epithelium

11 PAROTID SECRETION IN RUMINANTS on one side, or of the central end of one cervical vagus nerve, was largely confined to the ipsilateral gland. This suggests that the afferent connexions of the centres regulating parotid secretion are predominantly unilateral and that there is little communication between the centres on one side of the brain stem with those on the other. Similar conclusions were reached concerning the salivary centres of other species by Chatfield (1941) and by Magoun & Beaton (1942) as a result of direct stimulation of the medulla. The facility with which ruminant parotid secretion is excited by mechanical stimulation of the forestomach is not equalled in monogastric species, in which the receptors concerned with salivary secretion are largely confined to the mouth. Even in the latter group gastric receptors may have some influence on salivary secretion, for in the dog Oehl (1864) was able to excite reflex secretion of the submaxillary gland by introducing mustard, alcohol, etc., into the stomach, or by stimulation of the central end of the vagus nerve until nausea was apparent. In ruminants the parotid saliva plays an important part in ruminal digestion, in addition to aiding mastication, and mechanisms that relate the activity of the parotid gland to the physical conditions in the forestomach are clearly of value. Krasuski, Krynskaya & Kotlyarevskaya (1940) found that a variety of organic and mineral acids and salts would influence the rate of parotid secretion when introduced into the mouth or rumen, but in general the effects were small. The concentration and ph of the organic acids used to stimulate the rumen in the present experiments were well outside the values found in conscious sheep (Phillipson, 1942). Thus it is not yet possible to say whether parotid secretion is reflexly influenced by the chemical composition of the rumen contents of sheep under normal conditions. The parotid glands of goats and calves. The studies on the parotid glands of goats and three-month-old calves have shown that they closely resemble the parotid gland of the sheep in their innervation and reflex control. In calves less than a month old the parotid gland was able to produce little or no saliva. This gland has been found to be similarly immature in young goats (Kay, 1958a). The absence of parotid secretion in young calves has been noted and investigated by Krinitsin (1940) who suggested that the development of parotid secretion is related to the onset of ruminal digestion. However this may be, the immaturity of the parotid gland is probably of little consequence before mastication of solid food and ruminal digestion begin. SUMMARY 1. The secretion of parotid saliva has been examined in decerebrate and anaesthetized sheep and in anaesthetized goats and calves. 2. The secretory innervation consisted of preganglionic fibres in the glosso- 473

12 474 R. N. B. KAY pharyngeal and facial nerves. The post-ganglionic fibres were distributed to the gland in the parotid nerve, a branch of the buccal nerve. 3. Parotid secretion continued after section of the parotid nerve and following the injection of atropine, hexamethonium, Rogitine and Diamox. 4. Both the secretory and the vasodilator responses to stimulation of the parotid nerve were annulled by atropine. 5. Reflex parotid secretion was caused by: (a) mechanical stimulation of the mouth, the lower thoracic oesophagus, the cardia, the reticulo-omasal orifice and to a less extent the lips of the oesophageal groove, the reticulo-rumen fold and the epithelium of the reticulum; or (b) the introduction of acid into the mouth or rumen. 6. The afferent fibres concerned coursed from the mouth with the lingual and glossopharyngeal nerves and from the forestomach with the vagus nerves. 7. Little or no parotid secretion was found in calves less than one month old. My thanks are due to Dr R. S. Comline for his encouragement and advice, to Mr G. Baker and Mr D. Canwell for technical assistance and to the Lederle Laboratories for the supply of Diamox. This work was carried out during the tenure of an Agricultural Research Studentship and the expenses were met in part by a special research grant from the Agricultural Research Council. REFERENCES 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. BABICHEV, G. A., PERSTNOV, N. S. & KUtESCO, I. I. (1930). The work of the digestive glands in ruminants. Russk. fiz. Zh. 13, BERNARD, C. (1864). Du role des actions reflexes paralysantes dans la phenomiene des s6cretions. J. Anat., Paris, 1, CHATFIELD, P. 0. (1941). Salivation in response to localized stimulation of the medulla. Amer. J. Physiol. 133, CLARK, R. & WEISS, K. E. (1952). Reflex salivation in sheep and goats initiated by mechanical stimulation of the cardiac area of the forestomachs. J. S. Afr. vet. med. Ass. 23, COATS, D. A., DENTON, D. A., GODING, J. R. & WRIGHT, R. D. (1956). Secretion by the parotid gland of the sheep. J. Physiol. 131, COATS, D. A. & WRIGHT, R. D. (1957). Secretion by the parotid gland of the sheep: the relationship between salivary flow and composition. J. Physiol. 135, COLIN, M. G. (1886). Traite de Physiologie Comparee des Animaux. 3rd ed. T. 1, pp , Paris: Bailliere et fils. 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. (1951). Reflex contraction of the oesophageal groove in young ruminants. J. Physiol. 115, COMLINE, R. S. & TITCHEN, D. A. (1957). Reflex contractions of the reticulum and rumen and parotid salivary secretion. J. Physiol. 139, 24-25P. DENTON, D. A. (1957 a). A gregarious factor in the natural conditioned salivary reflexes of sheep. Nature, Lond., 179, DENTON, D. A. (1957 b). The study of sheep with permanent unilateral parotid fistulae. Quart. J. exp. Physiol. 42, ECKHARD, C. (1867). Beitrage zur Lehre von Speichelsekretion. Henles Z. rat. Med. 29, ECKHARD, C. (1893). Noch Einmal die Parotis des Schafes. Zbl. Physiol. 7,

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