pouch. In the majority of cases, however, in which there is a small
amount of food yolk and no special arrangements for parental care,
a larva is formed. No better group than the Mollusca can be taken
to illustrate this point, for in them we find every kind of development
from the completely embryonic development of the Cephalopoda,
with their large heavily-yolked eggs, to the development of
most marine Lamellibranchiata and many Gastropoda, in which the
embryonic period is short and there is a long larval development.
The Mollusca are further specially interesting for showing very
clearly cases in which, though the young are born or hatched fully
developed, the larval stages are passed through in the egg, and the
larval organs (e.g. velum) are developed but without function (e.g.
Paludina, Cyclas, Onchidium). As already mentioned, the larval
form of the Mollusca is the trochosphere.
2. Free-swimming larvae are usually formed when the adult is fixed. We need only refer to the cases of the Cirripedia with their well-marked nauplius and cypris larvae, to Phoronis with its remarkable actinotrocha, to the Crinoidea, Polyzoa, &c. There are a few exceptions to this rule, e.g. the Molgulidae amongst the fixed Tunicata, Tubularia, Myriothela, &c., among the Hydrozoa.
3. Internal parasites generally have a stage which may be called larval, in which they are transferred either by active or passive migration to a new host. In most Nematoda, some Cestoda, and in Trematoda this larva leads a free life; but in some nematodes (Trichina) and some cestodes the larva does not become free. (A. Se.*)
LARYNGITIS, an inflammation of the mucus of the larynx. There are three chief varieties: acute, chronic, and oedematous. The larynx is also liable to attacks of inflammation in connexion with tubercle or syphilis.
Acute Laryngitis may be produced by an independent catarrh, or by one extending either from the nasal or the bronchial mucous membrane into that of the larynx. The causes are various, “catching cold” being the most common. Excessive use of the voice either in speaking or singing sometimes gives rise to it. The inhalation of irritating particles, vapours, &c., and swallowing very hot fluids or corrosive poisons are well-recognized causes. It may also occur in connexion with diseases, notably measles and influenza. As a result of the inflammation there is a general swelling of the parts about the larynx and the epiglottis, the result being a narrowing of the channel for the entrance of the air, and to this the chief dangers are due. The symptoms vary with the intensity of the attack; there is first a sense of tickling, then of heat, dryness, and pain in the throat, with some difficulty in swallowing. There is a dry cough, with expectoration later; phonation becomes painful, while the voice is husky, and may be completely lost. In children there is some dyspnoea. In favourable cases, which form the majority, the attack tends to abate in a few days, but the inflammation may become of the oedematous variety, and death may occur suddenly from an asphyxial paroxysm. Many cases of acute laryngitis are so slight as to make themselves known only by hoarseness and the character of the cough, nevertheless in every instance the attack demands serious attention. The diagnosis is not, in adults, a matter of much difficulty, especially if an examination is made with the laryngoscope; in children, however, it is more difficult, and the question of diphtheria must not be lost sight of. The treatment is, first and foremost, rest; no talking must be allowed. The patient should be kept in bed, in a room at an even temperature, and the air saturated with moisture. An ice-bag round the throat gives much relief, while internally diaphoretics may be given, and a full dose of Dover’s powder if there be much pain or cough.
Chronic Laryngitis usually occurs as a result of repeated attacks of the acute form. It is extremely common in people who habitually over-use the voice, and is the cause of the hoarse voice one associates with street sellers. The constant inhalation of irritating vapours, such as tobacco smoke, may also cause it. There is usually little or no pain, only the unpleasant sensation of tickling in the larynx, with a constant desire to cough. The changes in the mucous membrane are more permanent than in the acute variety, and there nearly always accompanies this a chronic alteration of the membrane of the pharynx (granular pharyngitis). The treatment consists in stopping the cause, where known, e.g. the smoking or shouting. Careful examination should be made to see if there is any nasal obstruction, and the larynx should be treated locally with suitable astringents, by means of a brush, spray or insufflation. Overheated and ill-ventilated rooms must be avoided, as entrance into them immediately aggravates the trouble and causes a paroxysm of coughing.
Oedematous Laryngitis is a very fatal condition, which may occur, though rarely, as a sequence of acute laryngitis. It is far more commonly seen in syphilitic and tubercular conditions of the larynx, in kidney disease, in certain fevers, and in cases of cellulitis of the neck. The larynx is also one of the sites of Angeioneurotic oedema. In this form of laryngitis there are all the symptoms of acute laryngitis, but on a very much exaggerated scale. The dyspnoea, accompanied by marked stridor, may arise and reach a dangerous condition within the space of an hour, and demand the most prompt treatment. On examination the mucous membrane round the epiglottis is seen to be enormously swollen. The treatment is ice round the throat and internally, scarification of the swollen parts, and should that not relieve the asphyxial symptoms, tracheotomy must be performed immediately.
Tubercular Laryngitis is practically always associated with phthisis. The mucous membrane is invaded by the tubercles, which first form small masses. These later break down and ulcerate; the ulceration then spreads up and down, causing an immense amount of destruction. The first indication is hoarseness, or, in certain forms, pain on swallowing. The cough is, as a rule, a late symptom. A sudden oedema may bring about a rapid fatal termination. The general treatment is the same as that advised for phthisis; locally, the affected parts may be removed by one or a series of operations, generally under local anaesthesia, or they may be treated with some destructive agent such as lactic acid. The pain on swallowing can be best alleviated by painting with a weak solution of cocaine. The condition is a very grave one; the prognosis depends largely on the associated pulmonary infection—if that be extensive, a very small amount of laryngeal mischief resists treatment, while, if the case be the contrary, a very extensive mischief may be successfully dealt with.
Syphilitic Laryngitis.—Invasion of the larynx in syphilis is very common. It may occur in both stages of the disease and in the inherited form. In the secondary stage the damage is superficial, and the symptoms those of a slight acute laryngitis. The injury in the tertiary stage is much more serious, the deeper structures are invaded with the formation of deep ulcers, which may when they heal form strong cicatrices, which produce a narrowing of the air-passage which may eventually require surgical interference. Occasionally a fatal oedema may arise. The treatment consists of administering constitutional remedies, local treatment being of comparatively slight importance.
Paroxysmal Laryngitis, or Laryngismus stridulus, is a nervous affection of the larynx that occurs in infants. It appears to be associated with adenoids. The disease consists of a reflex spasm of the glottis, which causes a complete blocking of the air-passages. The attacks, which are recurrent, cause acute asphyxiation. They may cease for no obvious reason, or one may prove fatal. The whole attack is of such short duration that the infant has either recovered or succumbed before assistance can be called. After an attack, careful examination should be made, and the adenoids, if present, removed by operation.
LA SABLIÈRE, MARGUERITE DE (c. 1640–1693), friend and patron of La Fontaine, was the wife of Antoine Rambouillet, sieur de la Sablière (1624–1679), a Protestant financier entrusted with the administration of the royal estates, her maiden name being Marguerite Hessein. She received an excellent education in Latin, mathematics, physics and anatomy from the best scholars of her time, and her house became a meeting-place for poets, scientists and men of letters, no less than for brilliant members of the court of Louis XIV. About 1673 Mme de la Sablière received into her house La Fontaine, whom for twenty years she relieved of every kind of material anxiety. Another friend and inmate of the house was the traveller and physician François Bernier, whose abridgment of the works of Gassendi was written for Mme de la Sablière. The abbé Chaulieu and
