the gasometer and delivers it into the room or the street, and the air-chamber is suspended from a small pulley and counter-poised with weights varied according to the desired negative pressure. The

Sectional Diagram of S. Solis-Cohen's Apparatus for Pneumotherapy.

mechanical arrangement of pulleys and weights, the device for adjusting the weights, the lowering of the outer water-tank (now a

reservoir, and not for overflow), etc., are so obvious and so easily understood by looking at the figure ("Rarefied Air," Fig. 7) that a description in detail is unnecessary. Mr. Metzger has used a wire rope in preference to one of hemp. The combination of the two gasometers into one instrument is effected by means of a bellows which at the same stroke compresses air for delivery into one cylinder and rarefies air in order to exhaust the other cylinder. It is in reality two bellows mounted back to back on the same frame. The downward stroke of the lever compresses the upper bellows and expands the lower one. The recoil of the spring in the upper bellows expands that one and compresses the other. There is no communication between the two bellows. By means of a tube (2, 3) passing out of a window-board (1), the external opening being protected with wire gauze, the supply of air for inhalation is drawn from out of doors.

When both instruments are used together, being brought into communication through the lungs of a patient by means of a double stopcock connected with a face-mask or mouth-piece, the route for the air is as follows:

(a) From the street, (b) through the upper bellows, (c) to the compression gasometer, (d) thence to the lungs, (e) from the lungs, (f) through the rarefaction gasometer, (g) to the lower bellows, (h) which expels it into the room or into the street.

The compression and rarefaction are virtually made in the respective bellows. The gasometers act to a certain extent as reservoirs, but chiefly as intermediate regulating chambers, rising and falling to maintain a constant pressure in exact accordance with the weight placed upon them, and independent of the volume of air inhaled or exhaled. Their available capacity is a little more than 800 cubic inches.

For purposes of observation, sufficiently accurate for clinical comparisons, though not for physiologic data, the air-chambers carry a scale of cubic inches, enabling us to see the approximate volume of air inhaled or exhaled at each respiration. Apparatus for warming, chilling, drying, moistening, or medicating the air to be inhaled may be interposed at any desired point between the window and the patient. The most convenient method of medicating the air is by means of the sponge, as described. A variety of other methods are applicable. Thus a volatile medicament may be placed in or on the water contained in a Wolff bottle, through which the air is passed; or the spray from Oliver's vaporizer, may be thrown into

the inspiratory current by some such device as that represented in Fig. 8.

With the two gasometers described, the double bellows, and a pair of resistance valves, we are able to obtain the mechanical satisfaction

FIG. 8.

E

CODMAN &
SHURTLIFF.

G

Obq

S. Solis-Cohen's Apparatus for Medication of Compressed Air by Spray from Oliver's Nebulizer. F. Nebulizer containing medicinal solution; E, expiration valve; D, lever admitting air and turning on spray; A, attachment for compressed air (low pressure); c, attachment for compressed air (high pressure for spray); G, face-mask.

of all the conditions required for any of the following therapeutic expedients :

Inhalation of-1. Compressed air with exhalation into atmosphere.

Inspiration of Compressed Air. The inspiration of compressed air produces a sense of fulness in the chest, it facilitates the entrance of air into the lungs, and leads to an increase in the size of the thorax. According to Waldenburg, the enlargement of the chest amounts, even after a few inspirations, to nearly 3 cm. Expiration is also made easier, except when, by an exaggerated pressure, the lung is deprived of some of its elasticity.

The vital capacity of the lungs is increased from the beginning of the treatment; at first the increase is transitory, but after several hours it becomes permanent. The forces of expiration and inspiration are equally augmented. The increment of the vital capacity in cases of disease varies from 100 c.cm. to a litre at the end of several days' treatment.

In cases of very feeble expiration this will be found to increase more markedly than inspiration; but when the elasticity of the lungs is not strained the two forces ought to augment in equal ratio. It is probable that the development of the respiratory muscles is a factor in the production of these results, and that they cannot, therefore, be entirely attributed to an anatomical change in the lungs.

In the aged, in whom the costal cartilages are ossified, no appreciable modification is produced, either in the play of the respiratory movements or in the development of the thorax.

Gréhant, Ducrocq, Drosdoff, Waldenburg, Botschetschkaroff, Basch, and others who have studied the question, find that the increase in intra-thoracic pressure opposes an obstacle to the circulation, especially to the diastole of the heart, while the systole is favored by it. The result is a stasis in the veins and a fall of pressure in the aorta. But these effects are only noticeable during inspiration, and disappear during expiration.

The pulse, studied sphygmographically by Riegel and Frank, Waldenburg, Sommerbrodt, and Schreiber, is strong and full at the beginning of inspiration; later, as the pulmonary stasis diminishes and the arterial tension falls, it yields a higher and well-marked dicrotic tracing. The circulatory changes are, however, transient, although some authors have seen them persist for one-half to one hour.

Expiration into rarefied air produces mechanical phenomena exactly the reverse of those caused by inspiration of compressed air.

The diminution of intra-thoracic pressure brings about a compression of the thoracic walls, of which the patient becomes couscious

when the rarefaction amounts to one-thirtieth atmosphere. Extension is more complete and the volume of air given off, as measured by the spirometer, is augmented. This increase takes place at the expense of the residual air; it may reach a litre with a rarefaction of one-fiftieth to one-sixtieth atmosphere (15:13 mm. of mercury)an interesting fact that seems to indicate that the quantity of residual air is greater than is generally believed. Waldenburg has observed emphysematous patients expiring 5 or 6 litres of air (under the influence of a rarefaction of one-fortieth to one-sixtieth atmosphere) when their normal respiratory capacity did not exceed 2 to 3 litres.

The compression of the thorax evidences itself in a diminution of the circumference of the chest 2 or 3 cm. ; at the same time, under the influence of forced expiration, the respiratory muscles acquire greater play, the diaphragm rises higher, the excursions of the chest become more extensive, and soon the inspiration is also increased. The result is an augmentation of the vital capacity of the lungs.

The reduction in intra-thoracic pressure modifies the circulation, the phenomena produced being the reverse of those noted in the case of compressed air; the systole of the heart is impeded, while the diastole is favored; there is a tendency to the emptying of the veins and the filling of the arteries.

As the lung fills with blood the right auricle becomes distended, then, in turn, the left auricle and left ventricle; the pressure in the aorta rises, the jugular veins collapse and empty themselves. The study of these phenomena, made upon animals with the hemodynamometer, on man with the sphygmograph, have not yielded very decisive results. Nor can the results in animals be properly compared with those obtained in man.

It is important to note, from a practical standpoint, that by taking slow and prolonged inspirations the influences to which the circulation is subjected at the moment of expiration into rarefied air are weakened. By observing this practical point a marked action can be obtained upon the lungs, while that upon the heart is attenuated. The value of this is considerable in all cases where any exaggerated interference with the latter organ is to be dreaded.

The inspiration of compressed air and the expiration into rarefied air do not produce mechanical effects alone. Biedert holds that as the air strikes the respiratory passages with more or less force it provokes a certain degree of irritation.

The pressure to which the pulmonary tissue is exposed, as well as