CHAPTER II.. Nasal Cavities.

NASAL CAVITIES.

SIMPLE CORYZA.

Simple acute coryza, or inflammation of the mucous membrane of the nasal cavities, is of comparatively trifling importance in bovine animals, and, were it not for the possibility of gangrenous coryza being confused with it, there would scarcely be any necessity for a special description.

The onset of coryza is indicated by repeated sneezing and coughing, by congestion of the pituitary mucous membrane, which soon begins to secrete abnormally, and by difficulty in respiration, which becomes snoring or whistling.

The discharge, transparent at first, then mucous and muco-purulent, is abundant in quantity; the inflammation is arrested at this point or extends towards the facial sinuses, the pharynx and larynx; the eyes are swollen and watering, and almost all the characteristic symptoms appear which mark the onset of gangrenous coryza. Two signs, however, are wanting. The appetite is fairly well maintained, and the temperature little above normal. Simple coryza occurs at all times of the year in consequence of sudden chills, but is commonest in spring and autumn.

At first the distinction between this condition and gangrenous coryza can only be ascertained after taking the temperature.

=The prognosis= is absolutely favourable, and often in forty-eight hours every symptom disappears.

=Treatment= is confined to keeping the animals in stables at a suitable temperature, sheltered from draughts. Emollient fumigations and inhalations of turpentine, creosote, or eucalyptus oil rapidly check the more alarming symptoms. Warm drinks and foods and cooked roots are recommended.

In sheep, acute coryza as a consequence of chills, etc., occurs in autumn, but is more commonly due to a parasitic cause, viz., invasion of the nasal cavities by larvæ of certain œstridæ. During the succeeding winter it continues under the form of chronic coryza, as a result of the larvæ retaining their position in the sinuses.

Treatment of this parasitic coryza consists in trephining the sinuses and destroying the larvæ.

GANGRENOUS CORYZA.

Gangrenous coryza is a grave disease of diphtheritic character, which at first seems to be localised in the mucous membrane of the upper respiratory passages, but which exhibits a tendency to affect all the mucous membranes of the system.

The term “gangrenous coryza,” adopted in France, has been replaced in other countries, especially in Germany, by such descriptions as “contagious disease of the head,” and “malignant catarrhal fever of the ox.” Old writers describe gangrenous coryza as a disease common in the Jura, the eastern parts of France generally, and in the valley of the Saône. In reality this disease occurs everywhere, both in the centre, west and north of France, as well as in the eastern regions. Serious outbreaks frequently occur in Germany and Italy.

=Symptoms.= Gangrenous coryza assumes three different forms, which, however, only represent successive degrees of intensity of the attack. In the peracute form death occurs in three to five days, even when the characteristic signs are not all as yet apparent. In the acute, and by far the most frequent form, the disease lasts from fifteen to twenty days, and also ends in death in by far the greater number of cases. Finally, in the form usually termed chronic, the disease lasts from four to eight weeks, and most frequently ends in recovery.

Acute and peracute forms.—The onset is marked by very striking symptoms, which precede the local symptoms by some hours, or by a day or more.

The temperature rises rapidly from the normal to 103° or 105° Fahr. (39·5° to 41° C.), or even higher. Appetite and rumination are entirely suspended; the respiration becomes rapid and difficult, while the heart beats strongly and tumultuously; the muzzle is dry, the mouth hot, and salivation so abundant as to suggest an attack of foot-and-mouth disease. Fæces and urine are only passed at long intervals, and dysuria is present.

At first everything seems to indicate the development of an acute infectious disease; but soon afterwards appear local indications affecting the respiratory, ocular, digestive, urinary, nervous and cutaneous systems.

The respiratory symptoms are most important, and almost characteristic. Respiration becomes difficult, rough as in acute coryza, but soon assumes a snoring character, and is accompanied by a discharge, containing false membranes, from both nostrils.

The serous and muco-purulent discharge becomes rusty or reddish-brown, soon acquires a very fœtid smell, and is found to contain epithelial débris and yellowish-green false membranes. After the least effort to cough or the slightest touch on the membranes themselves—sometimes without any visible cause at all—epistaxis sets in, the blood being mixed with the discharge or simply escaping in the form of reddish strings, like that occasionally seen in glanders.

The mucous membrane of the nasal cavities is red, turgid, apt to bleed, and painful to the touch.

Percussion of the nasal cavities, sinuses, and even of the horns reveals everywhere exceptional sensibility.

Sometimes, but only in certain subjects, the lower portions of the head, including the muzzle, nostrils, lips and forehead, become infiltrated, as though the case were one of purpura. Thoracic complications are rarely absent, unless the disease is treated. Towards the end of the first week the respiration, still painful and snoring, becomes more rapid; and auscultation reveals at various points in the lungs areas of bronchitis and of broncho-pneumonia, indicated by bronchial râles, rattling breathing, and tubal souffles, etc. These complications are accompanied by attacks of coughing, which increase the discharge, and may threaten to end in suffocation. This happens when large masses of false membranes from the bronchi are thrown into the larynx and cannot readily be ejected through the glottis, which has been reduced in size by œdematous infiltration and inflammation.

Percussion is generally useless. The appearance of the eyes is also very significant. These symptoms develop simultaneously with the respiratory disturbance, and are marked by infiltration of the eyelids, œdematous conjunctivitis, and ophthalmia. The cornea becomes whitish, infiltrated, opaque, and sometimes shows ulcerative keratitis; or, on the other hand, it remains simply semi-transparent, and through it the media of the eye may be seen to have become opalescent. Ulcerative keratitis may develop rapidly and end in perforation of the cornea.

In certain rare instances examination with the ophthalmoscope has revealed the existence of exudative iritis; this condition may be complicated with syncchia, intra-ocular hæmorrhage, and result in permanent loss of vision.

These ocular symptoms are accompanied by continuous, abundant and prolonged discharge of tears, intense photophobia, and exceptional sensitiveness to manual examination, etc.

Digestive disturbance appears less important, and may be regarded as consequent on the febrile reaction, the general disturbance, or the condition of the respiratory apparatus. But complete examination will show that from the onset of the disease a special form of stomatitis occurs. From the first the mouth is hot and dry: soon afterwards abundant reflex salivation occurs, and the discharge, like that from the nose, becomes excessively fœtid. This stomatitis differs entirely from ordinary forms of stomatitis and from the stomatitis peculiar to foot-and-mouth disease, and is characterised by the necrosis of fragments of epithelium forming false membranes. These on being shed leave exposed numerous ulcers distributed over the tongue, cheeks, and lips. Neither vesicles nor pustules are produced, but merely false membranes of small dimensions.

The false membranes and ulcerations occur on the soft palate and in the pharynx.

When the patients survive for a certain time, croupal enteritis and ulcerative enteritis, sometimes accompanied by hæmorrhage, develop. The administration of enemata is followed by the passage of fæces containing considerable fragments of epithelium or of streaks of blood. From the outset these digestive complications are indicated by failure to ruminate, by cessation of peristalsis and by constipation, which is usually succeeded by abundant fœtid diarrhœa.

Functional disturbance of the genito-urinary apparatus is rarer, or at least more difficult to detect. The animals refuse drink; micturition seems to be suspended or very difficult. The urine may be albuminous or rose-coloured, in consequence of the presence of hæmatin; more rarely it is purulent or sanguinolent. There may also be urethritis, cystitis, pyelitis, and nephritis, with the passage of hyalin cylinders in the urine, although this is not always the case.

In females the mucous membrane of the vagina and lips of the vulva usually seem congested and œdematous; but it is rare to find diphtheritic false membranes, as on the buccal and nasal mucous membranes, etc. On the other hand, vaginitis and exudative metritis are common.

Cutaneous outbreaks also constitute important symptoms by which this disease is recognised. At points where the skin is fine, on the inner surface of the thighs, around the girth, on the inner surface of the forearm, and on the mammæ, etc., an exanthematous eruption occurs, followed later by the development of pustules, which at first sight might suggest cow-pox.

These pustules are prominently apparent, and can readily be detected on palpation. They are more or less confluent, hard, and without a peripheral œdematous zone.

In the case of the mammæ these pustules occur most commonly on the teats, are round or slightly oval in form, bright red in colour, and sometimes violet-red. They never become converted into vesico-pustules, as in cow-pox, or into vesicles; and in no way resemble the skin eruption peculiar to foot-and-mouth disease.

Certain nervous symptoms have also been described, comprising trembling, epileptiform convulsions, and paraplegia of the hind quarters.

Moussu has never seen nervous disturbance assume the form of epileptiform convulsions, and it is possible that the paraplegia referred to simply marks the last stage of the disease.

=Causation.= The essential cause of gangrenous coryza has not yet been definitely ascertained. Within recent years teachers of the highest authority have represented the disease as a general affection belonging to the hæmorrhagic forms of septicæmia (Nocard and Leclainche). Nocard has found ovoid bacteria in the false membranes of the larynx, and Leclainche a paracoli-bacillus in the mesenteric ganglia and the intestines, but the disease has never been reproduced in a characteristic and complete form similar to the clinical type.

Other microbes have also been described as occurring in the blood or discharges; but attempts to transmit the disease by using cultures or the different morbid products which observers have collected have invariably failed, and it has therefore been concluded that the disease is not contagious, but merely infectious.

Moussu does not regard this disease as a hæmorrhagic septicæmia, because the blood proves sterile unless grave pulmonary, intestinal or renal complications occur, and because the disease appears capable of being cured in a short time by simple methods. In the present state of knowledge he prefers to regard it as an infectious disease of diphtheritic form, at first localised in the upper respiratory and digestive tracts, always tending towards a grave toxæmia, and towards complications due to various other infections.

Even though direct contagion has not been proved, it is impossible to doubt that stables may become infected. This is sufficiently proved by the continued appearance of the disease when disinfection is neglected after the occurrence of the first case.

It is possible that the causes formerly assigned—viz., chills, the influence of draughts, and a morbid predisposition—may increase susceptibility in animals otherwise well cared for, but it is quite certain that infection of the stable is an important factor.

=Lesions.= The lesions vary with the complications, but those shown in the beginning are always identical. The mucous membrane of the nasal cavities is congested, inflamed, sphacelated, and ulcerated at different points. The turbinated bones and the ethmoid cells may become necrotic; in the larynx the region of the glottis is always most markedly affected; the mucous membrane becomes ulcerated in the neighbourhood of the vocal cords, and the tissues may become more deeply attacked.

In the trachea and bronchi the mucous membrane undergoes desquamation, and may become ulcerated at the points where false membranes have formed. The mucous membrane of the sinuses is always affected, but is rarely ulcerated.

Such complications as capillary bronchitis, broncho-pneumonia, and gangrene of the lung may be noted.

The mucous membrane of the mouth presents a violet-red or blackish-red colour; the tongue and gums are swollen, and ulcers as large as a lentil or a halfpenny may occur either singly or in a confluent form.

The genito-urinary apparatus reveals signs of croupal cystitis, submucous effusions of blood, vaginitis with the formation of false membranes, acute pyelitis, etc.

=Diagnosis.= When the symptoms are fully developed the diagnosis of gangrenous coryza is extremely simple, but the absence of some of these may justify hesitation in forming an opinion. If the examination is carefully carried out, it is always possible to distinguish this disease from simple coryza, which is only accompanied by trifling fever, and in which appetite is preserved; from foot-and-mouth disease, with its very characteristic buccal eruption and absence of lesions from the upper portions of the respiratory tract; and from contagious ophthalmia.

=Prognosis.= Up to the present time the prognosis has always been regarded as extremely grave, the mortality being sometimes as high as from 90 to 100 per cent., and moreover the cases which recover are invariably those of what is considered the chronic form. Sudden sinking of temperature during the disease is an unfavourable sign. From 1894 to 1900 Moussu never cured a single case, whatever his method of treatment; nevertheless, it now seems possible to regard the condition a little more hopefully, provided that no incurable complication occurs before the beginning of treatment.

=Treatment.= Of all the modes of treatment suggested—viz., anti-febrile agents, general stimulants, purgatives, diuretics, external stimulant applications, etc.—none have succeeded. Antiseptics injected into the nasal cavities, antiseptics given internally, milk diet, and all the methods hitherto suggested are equally useless.

The only treatment which appears to have achieved any degree of success is that of injecting physiological salt solution in large doses (up to six quarts per day, divided into three parts). All the animals treated by this method recovered, provided they presented no broncho-pulmonary complications.

The sole inconvenience of this treatment is the difficulty in carrying it out when the animals are at a distance from the practitioner. It is indispensable that they should be close at hand, in order that he himself may make the injections at the proper time. There is some reason for hoping, however, that serum from animals which have recovered will prove to be more active than saline injections.

This method of treatment should be followed up by the most rigid hygienic precautions. The mouth, nasal cavities and eyes should frequently be washed with antiseptic solutions. The stables should be freely ventilated, and the floors and bed kept in the cleanest possible condition, etc.

Whenever a case of gangrenous coryza is observed it should be isolated, and the stables should most carefully be disinfected.

TUMOURS OF THE NASAL CAVITIES.

Apart from actinomycosis of the upper jaw, tumours of the nasal cavities or of the sinuses are not frequent in bovine animals. They are, however, occasionally met with, and present symptoms which must be carefully studied in order to avoid errors of diagnosis. Usually they are of the nature of myxomata, more rarely of fibro-myxomata.

=Symptoms.= The dominant symptom is difficulty in breathing, both when moving and eating, a difficulty which is sometimes so considerable as to cause snoring respiration or roaring. Nevertheless, examination of the trachea and of the lung, visual examination of the lower portions of the nasal cavities, and manual examination of the pharynx, larynx and glottis give only negative results. It may even happen, as occurred in the case from which the illustration herewith was taken, that percussion of the maxillary sinus reveals normal resonance.

In the case of tumours of small size the forehead is not deformed. When, on the other hand, the tumour partly obstructs the nasal cavities it may thrust on one side the septum nasi and externally cause well-marked asymmetry of the face. Sero-mucous or muco-purulent discharge then occurs.

=The diagnosis= is somewhat difficult, for continuous or temporary roaring (or at any rate difficulty of respiration), being the dominant symptom, must be distinguished from roaring due to a laryngeal lesion like paralysis or tumour formation, from perilaryngeal compression due to enlarged retro-pharyngeal glands, and from tracheal or pulmonary lesions; and its origin must be located in the nasal cavities.

=The prognosis= is grave, in consequence of the difficulty of exploring the depth of these cavities and of the possible nature of the tumour. Nevertheless, in the case of simple myxomata permanent recovery usually follows extirpation.

=Treatment= is confined to extirpation, which is quite possible in the case of pedunculated tumours; in the case of sessile tumours free trepanation of the roof of the nasal cavities becomes necessary. The operation is quite safe.

PURULENT COLLECTIONS IN THE NASAL SINUSES. NASAL GLEET.

From the clinical point of view two varieties of this condition may be distinguished—inflammation of the mucous membrane of the maxillary sinus and inflammation of the mucous membrane of the frontal sinus and of the horn core. These forms of inflammation frequently lead to suppuration. The pus collects in the depressions and divisions of the frontal or maxillary sinus.

PURULENT COLLECTIONS IN THE FRONTAL SINUS.

=Causation.= In the majority of cases inflammation of the mucous membrane of the frontal sinus is produced by external causes: fractures of the horns and horn core accompanied by hæmorrhage into the horn core; fractures of the horn with exposure of the sinus of the horn core; wounds and violent blows on the occipital region or the frontal bone; cracks or depressions of the external wall of the sinus, etc.

In all these cases, whether blood is effused or the mucous membrane of the sinus is merely infiltrated with serum, infection may be produced by germs being deposited from the air passing through the nasal cavities and causing suppuration.

Purulent collections in the frontal sinus may result from continued irritation, like that due to a badly fitting yoke. They also occur as an accidental complication of general diseases like gangrenous coryza.

=Symptoms.= The catarrh or purulent collection in the sinus may be unilateral or bilateral, and the symptoms vary, according to the form which it assumes.

Unilateral collections.—Nasal hæmorrhage is often the first symptom, but this is often regarded as of little importance, because the formation of pus does not occur until very much later. The animal shows ill-defined pain, loses appetite, remains dull and somnolent, and carries its head on one side. The horn on the injured side is hot and sensitive, and at a later stage the eye becomes affected by contiguity of tissue. It is then swollen, closed, and watery; the conjunctiva is infiltrated, and somewhat inflamed. Sensibility and partial or complete dulness of the affected side may be detected by palpation and percussion. On the animal being made to cough, a yellowish or greyish-white discharge of very fœtid and sometimes putrid character escapes.

Bilateral collections.—Catarrh is rarely bilateral at first; but if the unilateral lesion is not treated, it affects the median septum dividing the two cavities, and the inflammation extends to the second sinus. The animal then shows dull pain, and exhibits marked depression; sometimes it appears quite prostrate. The head is carried low and inclined towards the ground, while the above-mentioned ocular symptoms and the indications furnished by palpation and percussion extend to both sides. Coughing produces momentarily a double discharge, which the animal disposes of after the fashion of horned cattle.

=Diagnosis.= The diagnosis only presents difficulty in the early stages. Later the warmth and sensitiveness of the horns, the partial dulness, offensive character of the discharge, etc., render diagnosis easy.

The disease is not likely to be mistaken for gangrenous coryza, despite the condition of the eyes, because it develops slowly, progressively, and without marked fever.

=Prognosis.= If treated early, unilateral or bilateral collections of pus in the sinuses are capable of cure, but later when bodily health is impaired and the local lesions of the mucous membrane very pronounced, there is less chance of success.

=Lesions.= The initial lesions consist in cracks, fissures, or fractures of the bones of the face or exostoses of traumatic origin. In other cases the mucous membrane alone is affected. As a result of chronic irritation it becomes thickened, inflamed, and ulcerated, and granulates freely. The depressions in the sinuses contain grumous, fœtid pus, which irritates the surrounding tissues and produces pain and general symptoms of cerebral irritation, which are sometimes very disquieting.

=Treatment.= Numerous methods of treatment were formerly recommended, such as absolute rest, bleeding, cold affusions, perforation of a horn, section of a horn, etc. None of these is of any value.

At first, provided only a certain degree of sensitiveness and simple catarrh without suppuration exist, antiseptic fumigations with tar, carbolic acid, thymol, etc., are useful; but later, when pus has formed, they are useless. At this period the only rational and efficacious treatment consists in trepanation. In unilateral collections three openings are necessary.

The first is an opening into the sinus of the horn core. It is made ⅜ to ¾ of an inch above the horn-secreting band of the horn. It must not be forgotten, however, in planning such an opening that the sinus of the horn core only exists in a rudimentary condition in young animals, and that it is scarcely possible to trephine the horns before the patient is three years of age.

The second opening is made towards the upper part of the frontal sinus about ¾ inch below the horn-secreting ring at the base of the horn and in a line with the axis of the horn core itself. Whatever the animal’s age and however little the sinuses may be developed, this opening is certain to expose the cavity of the frontal sinus.

In old animals where the frontal sinus is enormously developed, and where very large depressions exist in the orbital region, a third opening should be made just above a transverse line uniting the upper margins of the two orbits and inside the suborbital suture.

These openings having been made, treatment consists—firstly, in completely washing out the cavity with boiled water, cooled to 95° or 100° Fahr.; and, secondly, in injecting antiseptic and astringent solutions so as to check the formation of pus. Among such may be mentioned 3 per cent. carbolic solution, 5 per cent. carbolic glycerine, 2 per cent. solution of iodine in iodide of potassium, etc.

Whatever the drugs employed, the cavities should be washed out every day, first with plain sterilised water, and then with antiseptic solutions at the body temperature, since cold solutions often cause inflammation of the mucous membrane of the opposite sinus.

PURULENT COLLECTIONS IN THE MAXILLARY SINUS.

This disease is much rarer than that of the frontal sinus, and only within the last few years (Ries, 1899) has a really good description been given of it.

=The causation= is imperfectly understood. Injuries to the suborbital region and maxillary ridge, caries of the molar teeth, and inflammation occurring during the development of general diseases represent the principal causes.

The dominating and characteristic symptom of the presence of pus in the maxillary sinus consists in incessant snorting, accompanied by violent movements of the head and the discharge of purulent or muco-purulent material.

At the beginning of these attacks of snorting, which are produced by the reflux of pus from the sinus towards the nasal cavities, the respiration becomes snoring and rapid, and the animal makes sniffing movements as though the nasal cavities were partially obstructed. After these crises, the respiration again becomes silent.

Contrary to what has been observed in purulent collections in the frontal sinus, the discharge is unilateral, reddish yellow in colour, viscous in consistence, and is accompanied by clots of a gelatinous material or even of blood.

During the attacks of snorting, the discharge resembles that of croupal or pseudo-membranous bronchitis, but the material discharged is not moulded on the internal shape of the bronchi. The masses of discharge are irregular in form, and appear as though made up of fibrous tissue matted together. Attention having been attracted by the discharge, exploration of the trachea and chest reveals nothing; on an examination of the sinuses, however, palpation and percussion betray a certain amount of sensitiveness, together with partial or complete dulness, and the lesion is discovered.

=Diagnosis.= Confusion between pus formation in the maxillary and frontal sinuses can be avoided by careful examination.

=Prognosis.= The prognosis is not very grave; the animals maintain their appetite, but become thinner, and the condition shows no tendency to spontaneous cure.

=Treatment.= The only rational treatment consists in trephining, an operation practised immediately above the maxillary tuberosity and over the lowest part of the sinus (Fig. 164). This opening allows the cavity to be washed out and the sinus drained.

Antiseptic treatment exactly resembles that of purulent collections in the frontal sinus. Injections of astringents, dilute carbolic acid and iodine solutions, etc., are recommended.

ŒSTRUS LARVÆ IN THE FACIAL SINUSES OF SHEEP.

(FALSE STURDY.)

=Causation.= This disease of sheep, which sometimes produces vertigo resembling that shown in gid or sturdy, is produced by the growth of larvæ of Œstrus ovis in the frontal sinuses. The œstrus of the sheep assumes perfect insect form during the fine days of summer from July to September. The females swarm around the flocks and attempt to alight on the animal’s head close to the nostrils, where they deposit their eggs or larvæ. The larvæ crawl into the nostrils, thence into the nasal cavities, the meatus, and finally the sinuses, where they become fixed. In these sinuses they undergo complete development, increasing from a length of about ⅒ inch to from ¾ to 1 inch before their transformation into the nymph and perfect insect. They remain in the sinus for eight to ten months. When numerous and well developed they may fill the whole of the cavity.

=Symptoms.= It is easy for a careful observer to note the time at which the larvæ penetrate the sinus. During the hottest hours of the day the adult insects are continually hovering over the flocks, and on watching carefully one sees sheep suddenly become excited, tap with their feet, rub their faces against any hard, resisting object in the neighbourhood, plunge their nostrils into the dust, and snort violently.

When the larvæ have penetrated the nasal cavities they produce frequent attacks of sneezing by irritating the mucous membrane, and cause an intense sero-mucous and afterwards a moderate muco-purulent coryza. As long as the larvæ remain of small size, the apparent results they produce are insignificant, as during the first months of winter; but when they are numerous, and have become of considerable size, they cause symptoms which might suggest an attack of gid or sturdy.

Thus the bodily movements become spasmodic, the gait irregular, and the animals show attacks of vertigo. They stagger and fall, making convulsing movements, grinding their teeth and rolling their eyes, while frothy saliva escapes from the mouth, etc.

Death may occur during such attacks, which, however, are happily very rare. Most commonly the animals are simply dull and somnolent. They feed badly, carry their heads low, and sometimes hide themselves under the mangers or in corners.

In exceptional circumstances they bury their heads in the wool or carry them high in the air in walking, while they lift their front legs high, with a stepping movement.

=Diagnosis.= The diagnosis of parasitic invasion of the sinus in the sheep is rather difficult, because certain of the symptoms suggest gid. One never finds the signs of true gid, however, and, on the other hand, a certain amount of discharge and attacks of snorting always exist. Finally, gid (cœnurosis) only attacks young animals, whilst the larvæ of œstridæ are commonest in adults.

To confound the disease with verminous bronchitis is still less likely, for although a discharge exists in both cases, this is accompanied by cough in bronchitis, and only by sneezing attacks in infection of the sinuses.

Finally, in bronchitis, histological examination leads to the discovery of eggs or embryos of the strongyles. The diagnosis becomes very easy on post-mortem examination, the identification of the larvæ of œstridæ being extremely simple.

=Prognosis.= The prognosis is only grave when infestation is very pronounced. Most commonly the parasites complete their development without producing disquieting symptoms; as summer approaches they are expelled and recovery occurs.

=Lesions.= The only lesions consist in very active inflammation of the mucous membrane of the sinus, which appears excessively hypertrophied, and in the existence of larvæ. These develop in the midst of a magma of purulent, fœtid discharge. The number of parasites usually ranges from two to twenty, although Zürn declares that he has found as many as eighty in one subject.

=Treatment.= Many precautions have been suggested for preventing infestation. Many are impossible or difficult to carry out in current practice, even the soaking of the nostrils in empyreumatic oil, and the majority are useless. The only suggestion to which we attribute any importance consists in trying to prevent the perfect insects from obtaining a lodgment in cavities in the walls or roofs of sheep-sheds.

The really efficacious modes of treatment are also few in number, for the larvæ are so firmly lodged in the mucous membrane of the sinuses that they can only be detached after these have been trephined. The use of nasal injections, embrocations and powders, with the object of making the animal sneeze, are ineffectual.

Trepanation should not be performed until it is quite clear that the flock is badly infested, and when serious symptoms appear to threaten the lives of some of the animals.

The operation, although very simple, requires care on account of the thinness of the bones.

The anatomical directions are the middle line of the head, and a transverse line uniting the upper margin of the two orbits. The orifices are made in the two lower angles produced by the intersection of these lines (Fig. 169).

It is then easy to remove with the fingers or forceps the larvæ situated immediately below the point of trepanation, and afterwards to wash out thoroughly the cavities of the sinuses. If some lie at points which cannot be directly reached, they can be killed by injecting a little benzine and water. This proceeding is quite safe.