Anterior cervical region and neck

The anterior cervical region lies behind the vertical ramus of the mandible and includes the pharynx, soft palate, guttural pouch, parotid salivary gland, larynx, thyroid gland and parotid and pharyngeal lymph nodes. The clinically im­portant structures in the neck include the oeso­phagus and jugular veins, which are situated in the jugular furrow, and the trachea, located on the ventral aspect. The area is examined by inspection and palpation and in the case of the larynx and trachea by auscultation; needless to say both sides are included in the examination.

External inspection reveals whether any swell­ing is present, e.g. parotitis, suppurative lym­phadenitis of the parotid or pharyngeal lymph node, neoplasia of the lymph nodes or other tissues, empyema or tympany of the guttural pouch, etc. Direct inspection of the pharyngeal cavity is achieved by viewing it through the opened mouth or by endoscopy. The former method gives satisfactory results only in the dog and cat. Enlargement of the thyroid gland (goitre or neoplasia) causes local swelling in the anterior, ventral area of the neck. Local or general en­largement of the oesophagus (oesophageal diver­ticulum, foreign body obstruction, stenosis and paralysis) is associated with a swelling in the left jugular furrow.

External palpation in the larger animals is usually performed with both hands (Fig. 107), one to either side, stroking lightly at first and gradually increasing the pressure, because other­wise the animal will flinch even although there is no pain in the region. Such behaviour is more usual in nervous, temperamental animals. Pal­pation will reveal heat, swelling and pain, indi­cating inflammatory conditions, and deep-seated swelling which may be caused by foreign bodies or neoplasia. In all cases an attempt should be made to identify the tissue which is abnormal and, if possible, the nature of the affection. Painful conditions of the anterior cervial region may result in an extended carriage of the head and neck (Fig. 108), the object of which is to relieve pressure on the structures in this area. If the pain focus is unilateral, the head is inclined towards the unaffected side.

Internal Palpation of the Pharynx

In the ox, and to a lesser extent in the horse, the whole of the pharyngeal cavity can be ex­plored with the hand, protection against bites being afforded by the use of a suitable gag (Figs 102-105). This examination, in the horse, may require the administration of a sedative or narcotic drug in order to yield satisfactory results. The method is particularly applicable in the identification of foreign bodies, enlargement of the pharyngeal lymph nodes, which is mainly caused by bacterial invasion or neoplasia, and diffuse cellulitis of the region (consideration should be given to anthrax in the case of the last). A large increase in the circumference of the sphenoidal sinuses can sometimes be detected by this means.

When the hand is introduced into the isthmus of the fauces in healthy horses and cattle this structure is felt to contract, and the pharyngeal reflex is initiated (constriction of the pharynx followed by a swallowing movement and then mild retching); this reaction is absent, or weak, when there is paralysis of the pharynx, as in botulism, grass sickness, peripheral nerve dam­age (glossopharyngeal, pharyngeal branch of vagus, spinal accessory and hypoglossal) caused by trauma and pressure by a tumour or local pyogenic focus, etc.

The parotid salivary gland is situated subcutaneously in the anterior cervical region where it impinges on the lateral aspect of the vertical ramus. Its lobulated structure makes it easily and distinctly palpable. Swelling in the area of this gland does not, however, necessarily indicate disease of the gland itself (diffuse or local paro­titis); it may be caused by affections involving underlying structures (lymphadenitis of the paro­tid or pharyngeal lymph node, primary or meta-static neoplasia of the local lymph nodes, acute pharyngitis, etc.).

Guttural Pouch

This is a paired structure in the form of a large mucous sac which is a vertical diverticulum of the Eustachian tube; it is present only in equidae. The sacs are located between the base of the cranium and the atlas dorsally, and the pharynx ventrally; they are in apposition medially, but are separated by the ventral straight muscles of the head to some extent. The relationships of the guttural pouch with other cranial structures, particularly on its lateral aspect, are many and complex and in some instances fairly intimate, e.g. the external carotid, internal maxillary and external maxillary arteries, the internal maxillary and jugular veins. In addition the vagus, spinal accessory and sympathetic nerves, along with the internal carotid artery, are located in a fold of the dorsal part of the pouch. The guttural pouch contains air derived from the pharynx through the Eustachian tube; expansion and filling with warm air occurs during expiration, deflation and exchange with cold air takes place during inspiration. The mucous membrane lining the pouch is similar to that lining the Eustachian tube.

The guttural pouch is quite susceptible to infection which is usually introduced via the Eustachian tube. Not uncommonly infection fol­lows strangles or other respiratory tract infec­tions. Disease of the guttural pouch, which is invariably inflammatory and pyogenic or mycotic in character, causes, in severe cases, swelling of the anterior cervical region in the vicinity of the parotid salivary gland and, in some cases, pain. Tympanitis of the guttural pouches occurs occasionally in the newborn foal and in yearlings, as the result of inflammation or a congenital defect. In this case the unilateral or bilateral swelling is painless but tense. Severe distension of both pouches may cause dysphagia and dys­pnoea (Fig. 109). The swelling, which in most cases is unilateral, is soft and cushion-like, often reducible on pressure, and sometimes it omits a splashing (succussion) sound on percussion. This sound is produced by agitation of the free surface of a fluid exudate in the cavity or pouch. If the contents of the distended pouch consist of air or gas, percussion will evoke a resonant or tympanic note. Many cases of mycotic (Aspergillus spp.) infection of the guttural pouch do not produce distension and lateral swelling. Pharyn­geal paralysis resulting from nerve damage has been observed in some cases, while in others nasal haemorrhage of varying severity from mild epistaxis to profuse, recurrent and fatal has occurred following ulceration of the mucous membrane and erosion of the wall of one of the major arteries.

By means of the rhinolaryngoscope, the open­ing of the Eustachian tube into the pharynx, on each side, can be viewed directly and, by careful manipulation, the distal end of the instrument can be inserted into the slit-like aperture and advanced into the interior of the pouch. The pouch requiring examination may be indicated by noting some discharge seeping from the Eustachian orifice into the pharynx. The rhino-laryngoscope is a rather fragile instrument; horses undergoing examination should be given a sedative or narcotic drug. Radiological exami­nation, where practicable, may yield valuable information regarding the condition of the guttural pouches.

Larynx

In the examination of the larynx, external palpation is employed to establish its condition by noting the presence of pain, liability to cough­ing, any change in shape (neoplasia) and degree of rigidity (ossification). Swelling at the posterior part of the larynx may be associated with the thyroid gland. Auscultation over the larynx, in normal animals, reveals sounds which simulate those heard over the bronchial area (see p. 120). In local inflammatory states, when exudation has occurred, rattling or wheezing sounds are heard. When the glottis is constricted, the laryngeal sounds are whistling (stenotic). In such cases, a vibration or thrill (laryngeal fremitus) is recognized when the hand is placed firmly on the skin adjacent to the larynx. Constriction of the larynx occurs in oedema, originating in enlarge­ment of the thyroid gland as the result of local venous stasis, or as part of an allergic syndrome, or following inhalation of irritant fumes or smoke, in acute inflammatory diseases with local infiltration, e.g. anthrax in the horse and pig, and in gut oedema to a mild degree only. Partial obstruction may arise from inhalation of vomitus, and in horses with unilateral paralysis of a vocal cord (roaring or whistling), during exercise.

In the clinical examination for detecting para­lysis of the larynx in horses which on exercise have evinced roaring or whistling inspiratory sounds, a particular technique is employed. One side of the larynx is supported by the extended fingers and palm of one hand while the finger-tips of the other hand are pressed inwards, above the larynx, from the opposite side. In this way, if laryngeal paralysis is present, an abnormal inspiratory sound is produced by the narrowing of the rima glottidis which results. The stenotic sound arising from laryngeal paralysis occurs only during inspiration because it is during this phase of respiration that the flaccid, paralysed arytenoid cartilage and vocal cord are drawn into the lumen of the larynx, thus causing stenosis. Slight stenotic sounds can be accen­tuated by strenuous, forced exercise, such as driving or riding at a brisk pace, walking on three legs with a foreleg tied up or extended backing. Other causes of stenotic, upper res­piratory tract sounds include oedema of the pharyngeal mucosa, tumours such as lipomas, papillomas or carcinomas, or pedunculated re­tention cysts, when located near the epiglottis. In all these conditions the abnormal sounds are heard during both inspiration and expiration.

Laryngitis, characterized by abnormal inspira­tory sounds and respiratory rhythm, and coughing, occurs as part of the syndrome in all in­fections of the upper respiratory tract in animals. In those of an acute nature, palpation of the larynx will induce a pain reaction and intensify the severity of the cough and the degree of respira­tory embarrassment. Upper respiratory infection is a prominent feature in equine viral rhino-pneumonitis, equine viral arteritis, infectious equine bronchitis, equine influenza and strangles; infectious bovine rhinotracheitis and calf diph­theria; swine influenza; kennel cough (Klebsiella bronchiseptica) in dogs.

Laryngoscopy

The rhinolaryngoscope (Fig. 110) is one of the instruments used for endoscopy, i.e. the examination of the interior of a body cavity that is inaccessible to direct inspection. It consists of a tube some 75 cm in length, containing a built-in optical system by means of which it is possible to project and collect light rays at varying angles. The distal end of the instrument carries a small electric bulb which is supplied with current from a portable battery. The rays of light from the illuminated interior of a hollow organ fall on a prism and are thus directed into the tube of the laryngoscope.

The rhinolaryngoscope is more regularly used in equine practice, but it can be used in cattle. It is introduced through a nasal cavity. Premedication with a suitable sedative or tranquillizer is desirable and further restraint is achieved by means of a twitch or by holding up a foreleg. Thoroughbred and excitable horses should be given a general anaesthetic in order to ensure that a satisfactory examination can be made. After initial insertion the instrument is held so that its end is placed medially against the lower border of the nasal septum. It is then carefully inserted to the desired extent. The projecting portion of the instrument should, in all circumstances, be held with the hand steadied by a simultaneous grasp of the medial wing of the nostril (to avoid injury should the animal move its head).

With the aid of the laryngoscope, it is possible to examine thoroughly the whole extent of the nasal mucosa (rhinoscopy), and in addition the ethmoturbinates, the pharyngeal mucosa, the larynx, and the entrance to and interior of the guttural pouches; even the soft palate is some­times visible. It is possible in this way to diagnose swellings of the pharyngeal wall (oedema), haemorrhages (rhinitis, pharyngitis, purpura haemorrhagica), ulcers (glanders), exudate, neo­plasms and foreign bodies.

The larynx is situated on the floor of the pharyngeal cavity, towards its posterior part. It is possible to see the epiglottis, the arytenoid car­tilages, the vocal cords, the laryngeal ventricles and the upper part of the tracheal lumen. An important application of laryngoscopy consists in the demonstration of paralysis of the vocal cords (roaring or whistling). In this condition the vocal cords and larynx are seen to be asymmetri­cal and the mobility of one or both cords is lost. The left side alone is affected in the vast majority of cases. During forced inspiration the paralysed vocal cord is set in vibration. In catarrhal laryn­gitis, the mucous membrane is greyish-pink and coated with mucus. In tumours, and in oedema of the glottis, the outlines of the layrnx are in­distinct or completely unrecognizable, as the result of extensive swelling.

When the distal end of the laryngoscope is above the larynx, rotation to right or left, through an angle of 45° will reveal a vertically directed fold in the wall of the pharynx—the entrance to the Eustachian tube on that side. In suppurative conditions (empyema) of the guttural pouch there is a discharge of pus from the ventral commissure of the slit-like opening. If fitted with an angled lamp-mounting, the laryngoscope can be intro­duced into the guttural pouch itself, where nor­mally it is possible to see the divergence of the external carotid artery and its lingual branch, as well as the medial and lateral divisions of the pouch. In addition to accumulations of pus, blood, or concretions, diphtheritic membranes or ulcerations, it is possible to recognize absces­ses in the pharyngeal lymph nodes (guttural pouch lymph nodes) which may be discharging into the pouch.

On the upper aspect of the pharyngeal cavity, opposite the larynx, the ethmoturbinates appear in the form of a pair of large smooth convexities.

In the dog, and some of the other small ani­mals, the anterior part of the larynx can be exposed to view by opening the mouth with the aid of a suitable gag or loops of tape, drawing the tongue forward and depressing its root with a spatula or tongue depressor. An electric torch greatly facilitates the examination.

Thyroid Gland

The thyroid gland consists of two smooth ovoid structures joined by a narrow ventrally placed isthmus which is not detectable by pal­pation. As a rule the lobes of the normal gland are easily identified by this method. The two main lobes are situated laterally in close contact with the thyroid cartilage of the larynx and extend backwards to the proximal part of the trachea. This preliminary examination will reveal whether the thyroid gland is present; in rare cases it is absent because of a developmental defect.

Enlargement of the thyroid gland can be readily appreciated by palpation and, if it is considerable, can even be seen, as in goitre (Fig. 111). Goitre in its primary form is caused by iodine deficiency; the secondary form is attributable to interference with the absorption and utilization of iodine by factors such as excessive calcium intake, diets consisting mainly of Brassica spp. and gross bacterial contamina­tion of food or drinking water. The goitrogenic influence on the dam of diets containing low levels of cyanogenetic glycosides may be clini­cally apparent in newly born lambs (stillbirths, soft lambs). The position and nature of the thyroid swelling, which may be smooth, nodular, soft or firm, are readily determined. In well established goitre, the increased vascularity of the enlarged thyroid gland causes pronounced, local arterial pulsation and oedema of the sur­rounding tissues. Radiological examination, or the administration of radioactive iodine, may provide information to supplement the other findings. Alterations in the shape, size and con­sistency of the thyroid gland are the result of inflammation, neoplasia, injuries or endocrine dysfunction. Inflammation usually terminates in abscess formation; heat, swelling, pain and, in the later stages, fluctuation typify the condition. With tumour formation, the enlargement is irregular and eventually assumes considerable proportions. Depending upon which component tissue of the gland is primarily involved in the neoplastic state there may be other signs indica­tive of hyperthyroidism (increased heart and respiratory rates and, sometimes, exophthalmos).

Trachea

The trachea extends from the larynx to the hilus of the lungs. It consists of a tube-like struc­ture which is kept patent by a series of 50-60 in­complete, cartilaginous rings. In the neck the trachea is ventrally situated, and is related dorsally to the proximal part of the oesophagus, but mainly to the longus colli muscles. Laterally it is related to the lobes of the thyroid gland, the carotid artery, the jugular vein, the vagus, sym­pathetic and recurrent laryngeal nerves, the oeso­phagus (on its left side from the third cervical vertebra backwards), the tracheal lymph ducts, and the cervical lymph nodes.

The trachea is examined by inspection of the overlying skin and coat, which will reveal changes in shape or position, scars or tracheotomy wounds; by palpation, which is valuable in the detection of pain, local swellings, and deformi­ties; and by auscultation. Bronchial sounds (p. 120) are usually heard by auscultation over the trachea; they are usually somewhat greater in volume at this position. Moist rales indicate the presence of mucus, blood, exudate or other fluid in the trachea. Tracheal rales are detectable in tracheitis, bronchitis, parasitic bronchitis, severe pneumonia, pulmonary oedema and pulmonary haemorrhage. Sounds from this source can be detected in all the upper respiratory tract infec­tions referred to earlier in discussing the larynx. Stenotic or whistling sounds are audible when the mucous membrane is dry (early stages of inflammation), and when there is reduction in the size of the lumen of the trachea. This last occurs in constriction from tracheotomy or other wound scars, or pressure from a neoplasm or an enlarged thyroid gland. Radiography provides conclusive evidence as to the presence of neo­plasms, and the shape, position and course of the larynx and trachea. Tracheal auscultation resolves doubt as to the origin of abnormal sounds heard during auscultation of the lungs. If the sounds originate in the upper respiratory tract they will be heard only during inspiration. The methods employed to obtain a sample of fluid contents (sputum) of the trachea will be described later in this chapter.

Oesophagus

The oesophagus is a musculomembranous tube, varying in length according to the size of the animal, which extends from the pharynx to the stomach. At its origin it is medially situated, but at the fourth cervical vertebra it is located on the left side of the trachea, which relation­ship is continued as far as the third thoracic vertebra. In the dog the greater part of the oeso­phagus is located medially above the trachea.

The cervical portion of the oesophagus is examined in the depth of the jugular furrow; in rare cases it is situated on the right side of the neck. A number of diseases cause difficulty in swallowing (dysphagia); it usually results from physical obstruction by a foreign body or neo­plasm in the pharynx or oesophagus, although in occasional cases it is caused by local pain or inflammatory swelling. Oesophageal diverticulum, or segmental paralysis, invariably con­tributes to functional obstruction, which is manifested by dysphagia. The signs of dysphagia are forceful attempts to swallow, initially accom­panied by extension and then flexion of the head, with contractions of the cervical and abdominal musculature. They can be detected by observa­tion during and immediately after the ingestion of food or water. When deglutition occurs, the bolus can be seen passing downwards, along the left jugular furrow, as a mobile swelling in the oesophagus. When assessing the functional con­dition of the oesophagus, the first point to be determined, provided the animal is feeding, is whether deglutition occurs at all.

If dysphagia exists, apart from exhibiting the usual clinical signs, the animal takes an unusually long time to consume its food; slow feeding may, however, be caused by disturbances of consciousness, such as those arising from space-occupying lesions of the brain (hydrocephalus) and in the so-called 'dummy syndrome'. In herb­ivorous animals, finding completely masticated food in the manger indicates the occurrence of regurgitation, whereas the dropping of semi-masticated food from the mouth ('quidding') suggests a painful condition of the mouth. When the difficulty in swallowing is less severe, liquids can still be swallowed fairly readily, but not solids.

Abnormalities of the cervical portion of the oesophagus which cause changes in shape or contour are detectable by inspection or palpa­tion, e.g. impacted foreign bodies or tumours. In dilatation of a part or the whole length of the oesophagus (diverticulum as in Fig. 112, ectasia), or in constriction (stenosis), a swelling develops at the site of or anteriorly to the lesion while the animal is feeding. This swelling is reducible on pressure and disappears spontaneously after a variable time, but recurs whenever the animal feeds. Firm pressure at almost any point along the left jugular furrow may cause eructation, regurgitation and vomiting in certain conditions (oesophagitis, dilatation, spasm). Primarily oesophagitis may follow the ingestion of chemical or physical irritants and is usually accompanied by stomatitis and pharyngitis. Inflammation of the oesophagus is a concomitant, but usually un­recognized, feature of many specific diseases, particularly those causing stomatitis.

Dilatation of the oesophagus in the dog occurs in achalasia (cardiospasm, mega-oesophagus, ectasia) and in persistent right aortic arch or similar congenital vascular anomalies. Achalasia is due to abnormal innervation of the lower oesophagus and cardia because of absence of, or degenerative changes in, the neurons of the myenteric plexuses. A variable number of puppies in the same litter may be affected, suggesting the possibility of genetic inheritance. Adult dogs may occa­sionally develop the disease. The important clinical signs consist of persistent vomiting, which usually commences as soon as the puppies are weaned onto solid food. Nausea and retching do not occur. The cervical oesophagus is usually somewhat dilated and it fluctuates during breath­ing. The condition is diagnosed by endoscopic or radiographic examination employing a contrast medium (Fig. 113).

Vascular anomalies which cause dilatation of the oesophagus occur most frequently in the Alsatian breed. The most common abnormality of this type is persistent right aortic arch. The most obvious clinical sign is vomiting, which appears when the affected puppy begins to eat solid food, and becomes persistent by the time the animal is 3-8 months of age. Diagnosis is based upon consideration of the history and clinical signs, and radiographic examination em­ploying contrast medium (see Fig. 132, p. 142).

By introducing a suitable sound in the form of a stomach tube or probang (Figs 114, 115), i.e. a sufficiently flexible, firm, rubber, plastic or leather covered tube, it is possible to determine whether the oesophagus is patent and whether constrictions, foreign bodies, food masses, neoplasms, etc. are present. Enlargement of the posterior mediastinal lymph nodes in the ox, which may be caused by actinobacillosis, tuber­culosis or leucosis, may be detected by this method because the compression stenosis, which is produced by the enlarged node, offers some resistance to the passage of the instrument. The sound must be lubricated before use and should be introduced only when the head and neck are fully extended and the patient is adequately restrained. In the horse and in adult cattle it is introduced through the nasal cavity in the same manner as the laryngoscope and, more generally, in the ox and in other species, through the mouth, when a suitable gag (Fig. 115) is required to prevent the animal damaging the instrument with the molar teeth.

In the dog and cat, the lumen of the oesopha­gus can be viewed by means of a suitable illu­minated oesophagoscope (Fig. 116). By this means lesions affecting the mucous membrane and foreign bodies are readily appreciated. This method of examination can only be performed under general anaesthesia. The oesophagus in the dog is constricted at its origin by the existence of a prominent fold of mucous membrane at its ventral part. In addition, radiography and fluoroscopy may be employed in the examination of the whole extent of the oesophagus in small animals. For this purpose it may be necessary, in order to complete the examination, to administer a suitable contrast medium.

Coughing

A cough is initiated by reflex stimulation of the cough centre in the medulla oblongata by irritation of sensory receptors in one of various organs, particularly the respiratory mucosa. The stimulus may therefore originate in the pharynx, larynx, trachea, bronchi, pulmonary tissues or pleura. Coughing may also be initiated by irri­tation of the oesophagus, as in choking, or of an abdominal viscus, e.g. the stomach. The act of coughing consists of several stages; deep inspira­tion followed by approximation of the vocal cords; compression of the air in the lungs by vigorous forced expiration; sudden abduction of the vocal cords, which permits explosive expira­tion (the linear air velocity attains a speed of several hundred miles per hour). The purpose of coughing is the removal of excess mucus, inflam­matory products or foreign bodies from the respiratory passages. Fluid of low viscosity may, however, be forced back into the secondary and tertiary bronchioles by the sudden variations in air pressure. Coughing indicates the existence of primary or secondary disease of the respira­tory system, so that its existence should not be disregarded.

When the cough is infrequent, the animal may not exhibit it during the period of examination; it is then necessary to be able to induce the animal to cough when required. Coughing can be induced, particularly in the horse, by repeated application of light pressure to the larynx in the region of its junction with the first cartilaginous ring of the trachea (Fig. 117). Even the healthy horse, if not too restive, can usually be made to cough by this method. In inflammatory con­ditions of the larynx and pharynx, a cough is very easily provoked, but it is induced only with difficulty, or not at all, when the larynx is largely ossified (this state occasionally occurs in aged horses and cattle). If, in a case of spon­taneous coughing, pressure on the larynx fails to provoke a cough, its origin is probably else­where than in this region. Other methods of inducing coughing in large animals include applying intermittent pressure over the trachea in front of the entrance to the chest or giving a sharp blow with the hand, within the respiratory area, on the thoracic wall. Occlusion of both nostrils for 30-60 seconds—with the hands in the horse or with a folded towel in the ox (Fig. 118) —will also provoke coughing, as a result of hypoxia causing an immediate deep inspiration following the removal of the impediment to breathing. This applies particularly to diseases of the thoracic respiratory organs. In small animals, compression of the thorax between the hands, or lifting up a large fold of skin from the back behind the shoulders, so that the weight of the animal is almost supported, will usually induce coughing. An examination of this type should always be made when there is any suspicion of pulmonary disease.

It is important to determine the frequency and periodicity of coughing. In the early stages of an inflammatory disease of the respiratory tract, coughing is infrequent, but as the condition progresses it may become relatively frequent. Numerous coughs following one after another are described as a paroxysm of coughing. As a rule, coughing is painless, but in a few diseases, e.g. those in which pleurisy, acute catarrhal laryngitis or bronchitis occurs, it is accompanied by pain, in which case it is noticeable that the animal makes an effort to suppress the cough. A simple cough may be protracted or of short duration. Protracted coughs occur when there is inflammation of the vocal cords, as a result of incomplete closure of the glottis, and in chronic alveolar emphysema. The cough is short in acute bronchitis and in pleurisy, because of pain; in chronic tuberculous and similar forms of pleu­risy, owing to adhesions restricting the elastic recoil of the lungs; and in extensive pneumonia, because of the reduced volume of the expired air.

A cough may be loud, soft, croaking, wheez­ing, whistling, barking or tremulous (when the soft palate vibrates). Depending upon the volume of air expelled, the cough may be distinguished as deep or shallow. If the cough causes obvious expulsion from, or upward movement of secre­tion in, the respiratory tract, it is said to be productive or moist; if it is unaccompanied by movement of fluid material, it is said to be un­productive or dry. Deliberate expectoration of the secretion (sputum), as seen in man, does not occur in animals. That sputum has been coughed up into the pharynx is recognized by observing that, immediately after coughing, the animal makes the movements characteristic of chewing and swallowing. Small particles of sputum may be expelled involuntarily during coughing; this occurs when respiratory dyspnoea is relatively severe. In stalled or tied animals the particles of sputum may be seen on the wall in front of the animal.

The character of the cough is not dissimilar in all the diseases with which it is associated. In a number of conditions, however, the type of cough is sufficiently characteristic to arouse suspicion that a particular disease is in evidence, e.g. the infrequent, single, prolonged, unproduc­tive, hollow cough of a horse affected with chro­nic alveolar emphysema, and the dry, husky, paroxysmal cough of a calf with parasitic bron­chitis. Chronic bronchitis in the dog is associated with a barking type of cough. Irritation caused by the presence of Filaroides osleri in small nodules, involving the submucosal tissues, usu­ally at the bifurcation of the trachea in the dog, may cause a persistent harsh cough. In infectious equine pneumonia, the cough is infrequent, occurs singly and, in the early stages, is unpro­ductive. In catarrhal pharyngitis or laryngitis, in all species, the cough is frequent, paroxysmal, strong and painful, and very easily induced by pressure on the larynx or pharynx. In the exuda­tive stage of acute bronchopneumonia, it is frequent, paroxysmal, productive and explosive. A specific diagnosis, of course, cannot be made from the nature of the cough alone.

Microscopical Examination of Sputum

In certain diseases, notably bovine pulmonary tuberculosis, which because of the success of national eradication programmes is now very rarely seen, examination of the tracheal mucus by microscopic means may be diagnostic but a satisfactory sample of mucus from the respira­tory tract is often difficult to obtain, and further­more it must be remembered that excretion of the causal bacterium is variable. In the case of large animals, when tied up, it may sometimes be possible to obtain a mucus sample by affixing a large sheet of paper to the wall in front of the animal, and leaving it in position for some hours. Another method is to place the sheet of paper on the ground below the animal's head and then induce it to cough. More certain results are obtained by one of the following methods: swabbing the pharynx with a wad of sterile cottonwool attached to a suitable swab-forceps immediately after the animal has coughed and before the mucus can be swallowed (the rapid insertion of a mouth gag would be required for the method to be successful); administering a draught of cold water which will induce cough­ing by causing irritation of the pharynx; flushing the oesophagus free of food particles then pass­ing the sputum cup (Fig. 119) down the oesophagus, so that the respiratory mucus, which remain adherent to the mucous membrane after being swallowed, is collected in the container (this method is used mainly in cattle); inserting the sputum cup into the trachea, via the larynx, is also practicable in cattle, but it usually requires the administration of a potent ataractic drug; puncture of the trachea with a suitable cannula through which is then introduced a swab of cottonwool firmly attached to a short length of wire (adequate restraint and suitable sedation or local analgesia are necessary). In small animals a wire carrying a sterile cottonwool swab of appro­priate size can be introduced into the trachea from the mouth. It is usually essential to induce a state of narcosis, or even anaesthesia, to enable this to be achieved.

Helminth parasites, e.g. Dictyocaulus or Metastrongylus spp., Spirocerca spp., Filaroides osleri, CapUlaria aerophila, Crenosoma vulpis, Aleurostrongylus abstrusus, etc., may be seen in the mucus, or their ova identified by microscopical examination. The ova of lungworms are ovoid to round in shape, thin-shelled, and contain a developing larva (see Fig. 160b, p. 205). Failure to demonstrate the adult parasite, larvae or ova is not conclusive because they are not constantly present in the respiratory mucus from affected animals. A faeces examination (see pp. 198-201) usually gives more reliable results. In the dog, Filaroides osleri infestation can be identified by bronchoscopical examination.

Microscopical examination of suitably stained smears is very important in the diagnosis of pulmonary tuberculosis in animals with clinical manifestations suggestive of the disease. A nega­tive result should not be regarded as being conclusive. Bacteria of primary or secondary significance in relation to infections of the lower respiratory tract, such as Corynebacterium pyogenes, Pasteurella spp. streptococci, etc., may be observed, but specific identification would neces­sitate cultural and other methods of examination. Elastic fibres appearing in respiratory mucus may be of diagnostic significance when pulmonary gangrene is suspected. Fungi (Aspergillus spp., Candida albicans) may be of significance in asso­ciation with clinical manifestations of respira­tory disease, a situation which occurs occasionally in the horse and ox.