THYMUS GLAND, or simply the thymus (Gr. thymos, sweet thyme, because the gland was compared to the flower of this plant by Galen), one of those structures which, like the spleen, suprarenal capsules, and thyroid gland, are placed among the ductless glands. It is a temporary organ, and is caninionly stated to attain its greatest develop ment in relation to the rest of the body during the latter part of fetal life. " But this," says Dr. Carpenter, " is a mistake, for the greatest activity in the growth of this organ manifests itself in the human infant soon after birth. and it is then, too, that its functional energy seems the highest. This rapid state of growth, however, soon subsides into one of less activity, which merely serves to keep• up its proportion to the rest of the, body; but its increase is continued till the age of puberty is attained."—Principlea of Human Physiology, 6th ed. p. 143. After remaining stationary for some years, it gradually assumes, in well-nourished persons, the charac ters of a mass of fat. On examining- the gland when its growth is most active, it is found to consist of two lateral lobes placed in contact along the middle line, extending from the lower border of the thyroid gland to the cartilage of the fourth rib, and covered by the sternum and by the margins of the muscles passing upward from the top of that bone. The gland is of a pinkish gray color, soft and lobulated on its surfaces; and by careful manipulation it may be shown to consist of an assemblage of hollow glandular lobules, united together by connective tissue, all their cavities communicating with a central reservoir or main canal, from which there is no outlet. This arrangement is well seen in the gland of a calf. The thymus is about 2 in. in length, one and a half in breadth, and 4 lines thick, and at birth it weighs about half au ounce; its chemical con stituents are water, albumen, gelatine, sugar(?), fats, leuciue, sarkine, xanthine, and formic, acetic, succinic, and lactic acids, besides the ordinary inorganic salts—the num ber of the ingredients, many of them of rare occurrence elsewhere in the body, indi cating that important chemical changes take place in their structure. Its exact uses are unknown, but, like the other ductless or vascular glands, it doubtless plays some impor tant part in the preparation and maintenance of the blood. The albuminous nature of the juice of this gland, and the finely granular appearance it presents, indicate that a material is here being prepared which is to be rendered subservient to nutrition; and various facts which have been noticed in regard to its changes of bulk, (especially its rapid diminution in over-driven lambs, and its subsequent gradual redistention during rest, if plenty of food is given) strongly confirm these views.
The anatomy, physiology, and development of this gland have occupied the attention of three of the most celebrated writers of the present century: see sir Astley Cooper's beautiful monograph, On the Anatomy of the Thymus Gland, (1832); Mr. Simon's Physio logical Essay on time Thymus Gland, (1843); and prof. Goodsir's memoir "On the Devel opment of the Thymus Gland," in the Philosophical Transactions for 1844.
The only disease of this structure requiring notice is hypertrophy—a condition which. was supposed occasionally to induce suddenly fatal dyspncea (breathlessness) in children. There are, however, sound reasons for believing that there is no essential connection be tween the glandular enlargement and the suffocative paroxysms; because (1) the affection termed thymic asthma may occur with an abnormally small thymus; and (2) when a thymus, enlarged by malignant disease (encephaloid, for example) does occasion dyspncea, it is not sudden and paroxysmal, but constant in its nature. The disease is known under various other names, as larynosmus stridulus, spasmodic croup, and This bastard croup, as Dr. Watson calls it, is far more common than true croup, and is very liable to
be confounded with it. " In their most obvious symptoms, the two affections are much alike. The broad and essential difference between them is the absence in the spurious disorder of inflammation and of fever, and consequently of any concrete or other effusion from the mucous membrane of the air-passages. The child is seized all of a sudden, roused perhaps from its sleep, or checked in the act of sucking, by a catch, or interrup tion of its breathing, more or less complete. It strives and struggles to inspire, but to apparently unable to do so; at length the effort is successful, and the breath is drawn in with a shrill whistling or crowing sound, like that which characterizes the inspirations of croup, or of whooping-cough, and depending, no doubt, upon the same cause—a nar rowing (in this complaint, temporary) of the fissure of the glottis."—Tectures on the Prin ciples and Practice of Physic, 4th ed. vol. i. p. 866. The more complete the closure of the chink of .the glottis is, the more intense will be the symptoms. In severe cases the countenance becomes livid, the eyes fixed, and there is an entire suspension of the res piratory functions for a while. The child makes vehement struggles to recover its breath, and at varied intervals, from a few seconds up to a minute or longer, air is admitted through the glottis, now partially open, and this rush of air produces the characteristic sound. A fit of coughing or crying then often supervenes, and the attack terminates with some exhaustion. If, however, the glottis does not partially open, the child will die suffocated (or in popular language, in a fit) at the end of two, or at most three minutes, falling back pallid and exhausted in its nurse's arms. In association with these symp toms is often a contracted state of the flexor muscles of the thumb, fingers, toes, wrist, and ankle, giving to the foot an appearance like that of a club-foot. It has been ob served by Dr. Ley, who has written a volume, on this disorder, and other observers, that there is a frequent connection between child-growing and certain other affections, as (1) tumefaction of the glands in the neck and chest, and entanglement of the pneumo gastric nerve or its branches among these glands; (2) painful dentition, which is apt to produce glandular swellings of the neck; and (3) excoriations behind the ears, and in flamed and irritable scalp, which also occasion enlargement of the glands. The nerves passing from the enlarged gland to the nervous center convey the sensation of irritation; and the inferior laryngeal nerve, which supplies nearly all the muscles of the larynx, acts on the efferent or motor nerve, and excites spasmodic contraction of the muscles closing the aperture of the glottis. Hence the phenomena are those of reflex action.
During the paroxysm, the warm bath may be tried if it can be got ready at once. The application of hot fomeutations to the throat by means of a large sponge, is often very serviceable, and is usually more accessible than the bath. The muscles sometimes relax when cold water is freely sprinkled over the chest and face, and these simultaneous ap plications of hot and cold water are by no means incompatible. The subsequent gene ral treatment must depend upon the exciting cause, on the painful dentition, the erup tion of the head, etc. The state of the bowels and of the skin must always be carefully regulated, and change of air is always advisable. Phosphate of lime, in doses of from 5 to 10 gr. 3 times a day, administered in chalk mixture, has been strongly recom mended by Dr. W. Budd in this disease, and is well deserving of a trial.