quite interrupted; the motion of the abdominal walls on either side is usually not affected.

In peritonitis, if the disease be general, the abdominal motion is universally diminished; if it be partial, the diminution of the respiratory motion is most marked over the immediate seat of the inflammation.!

From the foregoing, it is apparent that the modifications of the respiratory movements in disease are of great value in aiding diagnosis, since although the nature of disease is not indicated by them, yet its seat is at once pointed out. In the majority of cases, the indications afforded by the senses of touch and vision will be sufficient; but in obscure examples of pulmonary disease, the observations will be rendered more minute and accurate by the aid of the chest measurer.

4. SUCCUSSION.

Succussion is performed by gently but abruptly pushing the patient's trunk backwards and forwards, or, by the patient himself making the same movement, while the observer's ear is applied to the walls of the thorax. It is employed to detect the sound of thoracic fluctuation, produced by the violent collision of air and liquid in a cavity of somewhat large dimensions, and compared by Dr. Walshe to the splashing of water in a party-filled decanter held close to the ear r; the precise tone, however, will vary with the density of the fluid, and the proportion of fluid and air present. The sound of thoracic fluctuation may also be accompanied with metallic tinkling. It is elicited in cases of pneumo-hydrothorax, with pulmonary fistula; or, very rarely, in pneumo-hydrothorax, when no fistulous communication exists between the lung and pleura; and in phthisis, when the tubercular cavity is large and partly filled with fluid.

5. SPIROMETRY.

The spirometer is an instrument for measuring the volume of air expired from the lungs, the construction of which, as well as the way in which it is to be used, is fully explained in Chapter II, Section 3.

The extent of the movements performed by the thoracic

1 Dr. Sibson : On the Movements of Respiration in Disease. MedicoChirurgical Trans. Vol. xxxi, p. 376; and Prov. Med. and Surg. Journal, 5th Sept. 1849.

VITAL CAPACITY AS AFFECTED BY HEIGHT. 155

boundaries for the purpose of respiration, admits of three degrees of modification:

a. Extreme expansion (inspiration).

b. Extreme contraction (expiration).

c. Intermediate condition (ordinary breathing).

The first two movements displace a larger, and the third movement a smaller volume of air. The spirometer measures collectively these three volumes of air; that is to say, the most complete voluntary expiration immediately following the most complete inspiration, which Dr. Hutchinson denominates the "vital capacity," or the "vital volume." The vital capacity volume is the limit of all the requirements for air which man can require; the ordinary breathing is a quiet, gentle, and more limited movement. The ordinary breathing movement may be considered, then, to have "a spare margin which is ever at command-a margin absolutely necessary to health. When we cannot command this margin, i. e., extend the ordinary breathing movement into the extraordinary breathing movement, the body is incommoded, and our well-being suffers relative to the degree of change in the thoracic mobility." The spirometer not only measures this margin together with the ordinary breathing movement, but it also determines the permeability of the lungs to air. Dr. Hutchinson chose to found his observations upon the vital capacity volume rather than upon the ordinary breathing volume, because the former is from twelve to twenty times greater than the latter, and an error in a few cubic inches in the larger volume is of little consequence; while an error of a few cubic inches in the ordinary breathing volume is of such importance as to disguise the correct measurement of the natural breathing volume, and is sure to occur from the nervousness or stupidity of the person examined.

The vital capacity volume is affected by height, by attitude, by weight, by age, and by disease.

The Vital Capacity as affected by Height.-From a very large number of experiments, Dr. Hutchinson has deduced the curious fact that the height of an individual is the chief condition which regulates his vital capacity, and he lays down the following rule: That in the erect position, for every inch of stature from five feet to six feet, eight additional cubic inches of air, at 60° Fahr., are given out in one volume, by the deepest expiration, immediately following the deepest inspiration. This table is intended to show the capacity in health and in the three stages of phthisis.

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

This reads thus: A man between 5 ft. 7 in. and 5 ft. 8 in.
in height, should be able to breathe, in health, 230 cubic
inches; in the first stage of consumption this will be reduced
to 154; in the second to 131; and in the third to 108 cubic
inches.

Weight as affecting the Vital Capacity.-In examining
diseases of the lungs, the indications afforded by the weight of
the individual are invaluable. One of the first signs of disease,
generally, is loss of weight; a steady loss always precedes
consumption, and is the earliest symptom of tubercular disease.
Dr. Hutchinson has observed, that a slow and gradual loss is
more serious than a rapid and irregular diminution. A person
may lose weight, but he cannot do this gradually without some
severe exciting cause.

Weight in excess begins mechanically to diminish the
breathing movements when it has increased to 7 per cent.
beyond the mean weight; and from this point the vital capacity
decreases 1 cubic inch per lb. for the next thirty-five lbs. The
ordinary weight increases with the height, probably about 64
lbs. per inch of stature. It is unnecessary, however, to make
the correction for weight, unless it be much in excess. From
an examination of 2650 healthy men at the middle period of
life, Dr. Hutchinson has deduced the following table :
This table reads:-A man 5 ft. 8 in. should weigh 11 st.
1 lb., or 155 lbs. (14 lbs. = 1 stone); he may exceed this by
7 per cent., and so attain 11 st. 12 lbs., or 166 lbs., without
affecting his vital capacity; beyond this weight his respiration
becomes diminished.

=

Age as affecting the Vital Capacity.-The vital capacity is found to be at a maximum between the ages of thirty and thirty-five, though the effect of age is not very manifest until a person has attained fifty-five years, when the capacity diminishes sufficiently to render it necessary to make a subtraction. This we must do according to the annexed table:

Thus it appears that a man of 5 ft. 8 in., of the mean weight, may be expected to breathe 230 cubic inches until the age of fifty-five, 219 cubic inches from fifty-five to sixty-five, and 212 from sixty-five to seventy-five years of age.

In all the foregoing calculations, it is supposed that the patients are dressed in ordinary attire. We therefore have to make no allowance for boot-heels, weight of dress, &c. It may be remarked, however, that M. Quetelet estimates the average

weight of the clothes, at different ages, as one-eighteenth of the total weight of the male body, and one-twenty-fourth of the total weight of the female.

6. PERCUSSION.

For the invention of the method of percussion-so to speak -we are indebted to Avenbrugger, who published at Vienna, in 1761, his "Inventum novum, ex percussione thoracis humani, ut signo, abstrusos interni pectoris morbos detegendi," a treatise which remained unread until Corvisart translated it and brought it into general notice.

Percussion-the act of striking the parietes of the cavities of the body in such a manner as to enable the examiner to judge of the density of the subjacent parts-is one of the most important means of physical diagnosis in diseases of the chest. It is said to be immediate or direct when nothing intervenes between the percussing agent and the part percussed; mediate when some solid substance-as the finger or a plate of ivory-is placed upon the part to be explored, and the blow made upon such substance. In the present day mediate percussion is generally employed; the four fingers of the left hand, pressed firmly against the chest, serving as a pleximeter, while the ends of those of the right hand, brought together into a line, form the plessor or percussor. Immediate percussion may be performed by striking the chest with the palmar surface of the fingers. In practising percussion, it is best to strike first on one side of the chest and then on the corresponding spot of the other side, in order to compare the results; since our estimate of the presence or amount of disease is determined more by the relative degree of dulness or resonance on the opposite sides, than by any absolute degree of dulness; in doubtful cases the observation should be repeated many times, and in various postures. The strokes also should be made quickly, smartly, and uniformly, and at right angles to the part percussed; and the hand should be moved from the wrist alone, the forearm and arm being held motionless, as the strokes will be better regulated, and fall more uniformly on the parts struck.

In percussion, if the chest be struck over a portion of healthy lung, a hollow or clear sound will be produced; if over a portion of lung which has lost its spongy character and is void of air, or in any way solidified, either by pressure from without-as in pleuritic effusion, or by deposit withinas in pneumonia or pulmonary apoplexy, then only a dull,