for the following reagents: nitric acid, sulphuric acid, acetic acid, hydrochloric acid, liquor potassæ, liquor ammoniæ, a saturated solution of nitrate of barytes, solution of nitrate of silver (one drachm of the crystallized nitrate to the ounce of distilled water), solution of oxalate of ammonia, alcohol, and rectified ether. Should the practitioner prefer a more portable case, he can purchase Highley's Cabinet of Apparatus and Reagents, as selected by Dr. Lionel Beale, in which he will find, urinometer in case, test-papers, graduated 2 oz. measure, pipette, stirring-rod, microscopic slides and thin glass, watch-glasses, test-tubes, tube-holder, brass-forceps, platinum foil, spirit-lamp with wire ring, and seven capped dropping bottles for the following reagents: nitric acid, acetic acid, ammonia, potash, nitrate barytes, nitrate silver, and oxalate of ammonia. With these agents he will be enabled to make a clinical examination of the urine, blood, sputum, &c., as far as it is necessary to do so in the practice of medicine for the purposes of diagnosis. For the mode of making a chemical analysis of the blood and secretions, see Chapter XI.

SECTION 3. THE SPIROMETER.

Under the designation of the pulmometre, the spirometer has been known for the last half century, but it was of no practical utility until the vital capacity of the lungs was ascertained by the laborious researches of Dr. Hutchinson.'

Hutchinson's Spirometer.-This instrument-somewhat resembling a small gasometer-consists of a cylindrical vessel of japanned zinc, about two feet and a half high and two feet in circumference, capable of holding many pints of water. Into it is inverted a cylinder or receiver-somewhat smallerwhich is counterpoised by weights; in its cover is inserted a movable plug. Communicating with the smaller cylinder is a tube, having an elastic tube and mouth-piece attached. A graduated scale is fixed to one side of the instrument, extending some distance above the top of the large cylinder. On respiring through the mouth-piece, the air passes into the lesser cylinder, and causes it to rise by displacing the water; an indicator attached to it marks on the graduated scale the number of cubic inches of air expired. We are thus enabled readily to measure the volume of air expired from the lungs.

When the vital capacity is to be tested by this apparatus, the patient should loosen his vest, stand perfectly erect, take as deep an inspiration as possible, and then place the mouth

See Medico-Chirurgical Transactions, vol. xxix, p. 138.

piece of the spirometer between his lips. The observer having opened the tap, the patient empties his lungs, making the deepest possible expiration, at the termination of which the operator turns off the tap, thus confining the air in the receiver. The receiver is then to be lightly depressed until the surfaces of the spirit in a bent tube on the outside of the instrument are on a level with each other, when the vital capacity may be read off from the scale.

Coxeter's Portable Spirometer is of much more simple construction than the preceding, and is so compact that it can be easily carried in the pocket. It consists simply of two flexible, inelastic, air-tight bags, one being much larger than the other and communicating with it by means of a piece of tubing provided with a stopcock. It may be best compared to the human stomach and duodenum, supposing that at the cardiac orifice a mouth-piece, tube, and stopcock are attached; another stopcock at the pyloric orifice, by which the opening into the duodenal continuation can be opened or closed; and a third stopcock at the termination of the duodenal portion, by opening which this part can be emptied of its contents: we must also imagine the duodenum to be graduated, and to be capable of containing exactly fifty cubic inches of air. Suppose now that the two bags have been compressed in our hands, the air expressed from them, and that they are kept empty by closing the stopcocks; if we take a deep inspiration, apply the mouth-piece, open the stopcock and expire, the expired air will be forced into the large bag, where we retain it by closing the tap; by opening the communication with the duodenal portion, and letting it fill with the expired air from the large bag, we obtain precisely fifty cubic inches; then, by closing the communication, and opening the escape valve, we have the duodenal part again empty, and ready to measure another fifty cubic inches, or thirty, or forty, as the case may be; and so we proceed until the whole volume of the expired air in the large bag has been ascertained.

Dr. Pereira's Spirometer. This instrument is much the same in principle as Dr. Hutchinson's. It consists of a large glass cylinder, suspended by means of a cord, in a reservoir of water, the cord passing over a pulley, and having a weight attached, so that by careful adjustment the cylinder may balance in any position. A pipe, forming the continuation of the tube through which the patient has to breathe, rises in the bell-glass above the level of the water; and by forcing the air through this tube, the vessel will ascend, and indicate, by a graduated scale affixed, the quantity of air passed

into it.

SECTION 4. THE TAPE-MEASURE, STETHOMETER,
PLEXIMETER, STETHOSCOPE, ETC.

The Common Tape-Measure.-A common measure thirty-six inches in length, fixed in a small German-silver box, and made to act by a spring, will be found useful in the diagnosis of diseases of the lungs. To ascertain the circumference of the chest we pass the tape round it, over the region of the nipples; should the patient have his shirt and flannel jacket on, we must make an allowance of a quarter of an inch for each of these articles. To learn the mobility of the chest, we pass the measure as just directed, request the patient to fill his lungs as much as possible by taking a deep inspiration, and note the number of inches on the measure, this being of course the greatest circumference; we then, without moving the tape, make him expire to his utmost, and noting the number of inches, we shall have the minimum circumference; the difference between the maximum and minimum will give us the mobility of the chest. In healthy persons, of ordinary weight and middle age, the average mobility is three inches, very rarely extending to four.

The Stethometer.-An instrument, called a stethometer, for measuring the expansive movements of the thorax during inspiration, and for ascertaining the difference in the mobility of opposite sides of the chest, has been invented by Dr. Richard Quain. It is a small machine about the size of a watch, with a graduated dial, and an indicator; a silk cord passes out of the side of the case and is connected by an axle with the indicator, which is capable of moving round the dial plate. The cord being extended from one fixed point on the chest to another, the extent of the respiratory movement becomes manifested by the tension made on the cord being communicated to the indicator, which thus shows the degree of expansion during inspiration, and of contraction during expiration. It is obvious that not only will the mobility of the chest be thus shown, but comparisons can also be readily drawn of the action of different parts of the chest, giving this instrument, therefore, advantages over the common tape-measure.

Dr. Sibson's Chest-measurer.-This instrument-somewhat resembling Dr. Quain's-is useful for ascertaining the diameter of the chest, and for accurately measuring the movements of respiration to the hundredth part of an inch. In form it resembles a watch, with a small bar or rack protruding from its lower part. This rack, when raised by the

moving walls of the chest, moves, by means of a pinion, the index on the dial; one entire revolution of the index showing one inch of motion in the chest, and each division indicating the hundredth of an inch.

The chest-measurer can be readily applied to any part of the body, and, by successive applications of it over the chest and abdomen, all the movements of respiration can be observed with great facility. It indicates the rhythm of respiration, showing whether the expiration be equal to, or longer or shorter than the inspiration; the character as well as the extent of motion may be read off from the dial. By it, also, we can perceive the exact amount of chest-movement, both during tranquil breathing and the deepest possible inspiration and expiration. It thus tells indirectly (though less accurately) the extreme breathing capacity of the chest, which is rendered directly and exactly by Dr. Hutchinson's spirometer; its inferiority in this respect is, however, in some measure counterbalanced, by its possessing the additional faculty of localizing the diminished movement, if it be local, and so pointing to the diseased part; or of showing it to be diffused over the whole breathing apparatus, if the disease be more general.

Plessors, Pleximeters, &c.-In practising percussion, the fingers, as a general rule, are superior to any artificial instruments. Occasionally, however, a small hammer tipped with gutta percha, or a thimble headed with the same material, may be useful as a plessor (anoow, I strike), and may enable us to produce a clearer stroke; these may be employed either for striking on the index or middle finger as a pleximeter (Toow, and μerpov, a measure), or the pleximeter may consist of a small thin disk of ivory-as used by M. Piorry, or of wood, or of India-rubber, each being provided with lips which are used as handles. In some regions it is not always possible to percuss with the fingers with an equal degree of force on the two opposite sides, as in the axillæ. In such instances, Dr. Sibson's ingenious spring pleximeter may often be used with advantage, since, by it successive strokes are produced exactly of equal force, which ought consequently to elicit, under similar circumstances, exactly the same sound. Another advantage possessed by this instrument is the ease and precision with which it can be applied over the clothes, in which respect it will be found useful in percussing children and females, as well as men during the cursory examination usually made at the life-assurance office.

The Stethoscope.-The stethoscope (Tos, the chest,

and exori, to examine) is a cylinder of soft wood (generally. cedar) from four to eight or nine inches in length, pierced through by a longitudinal canal about a quarter of an inch in diameter, and having one extremity large and flat as an earpiece, while the other is much smaller and funnel-shaped for application to the thoracic walls. The object of such an instrument is to collect and convey to the ear of the observer, the vibrating impulse of the air, or of the solid walls of the thorax, occasioned by the perpetual movement within.

General Observations. From the numerous diseases which derange the acts of respiration, and from the great variety of these disturbed movements, it is clear that we cannot form a diagnosis from the mere observation of the exaggeration, restraint, or arrest of any special movement. We are not, therefore, directed to any final diagnosis by the indications derived from the spirometer, the chest-measurer, the educated eyesight, or the touch; by these we are merely led to make correctly the first step; from them we only learn that there is derangement, and in some cases its seat. By the aid of percussion we advance still further; while by the practice of auscultation-aided by a knowledge of all the symptoms-we are enabled, in the great majority of cases, to give an accurate opinion as to the situation and exact nature of the disease, whether it be fixed in some part of the organs of circulation or of the organs of respiration. What I would insist upon, therefore, is this-that neither of the instruments described in the preceding paragraphs must be trusted to alone; neither the spirometer nor the stethoscope may be leant upon as a crutch, but merely employed as a staff to explore the way; auscultation and percussion are no substitutes for other methods of diagnosis, they are merely most valuable auxiliaries.

SECTION 5. THE DYNAMOMETER.

The dynamometer is an instrument, invented probably by Mr. Graham, but improved by M. Regnier, for measuring the comparative muscular strength of man and animals; and although not used perhaps in the practice of medicine, at least to any extent, still it deserves mention. It consists of an elliptical steel spring, of about twelve inches in circumference, connected with an index and needle, so that when by pressure the two sides are made to approach each other, the needle moves upon a portion of a circle furnished with a scale of kilogrammes, and one of myriagrammes. For example,