patients to remain in them for a considerable length of time with high degrees of pressure and rarefaction, and provided with the necessary machinery for producing these changes, are very expensive and cumbersome, so much so, indeed, that they can not be introduced into general practice outside of institutions standing on a firm financial basis.

When placed in such a chamber, with a pressure of two or three atmospheres, the first effect is to diminish the frequency and increase the depth of respirations. The quantity of oxygen absorbed is materially increased; the frequency and volume of the pulse are lessened after the subsidence of the primary excitement. Blood is driven from the cutaneous and mucous capillaries to the tissues in the cerebro-spinal canal and other tissues similarly located. The diaphram is depressed by the diminished volume of intestinal gases, resulting in increased pulmonary capacity, as fully verified by spirometric tests.

Diminished density leads to expansion of intestinal gases, and elevation of the diaphragm. There is diminished vital capacity and increased respiratory frequency. The frequency and volume of the pulse are increased. The quantity of blood in the lungs and skin is increased, with concomitant anæmia of the brain, spinal cord and other deep-seated organs.

Other parts of the body, aside from the lungs, may be subjected to the action of a localized pneumatic differentiation. Pneumatic chambers can be made to fit a part or all or any of the extremeties. Increase of pressure surrounding a limb could be utilized for the purpose of relieving hyperæmia or inflammatory conditions. Edema could be relieved in like manner by a carefully regulated increase of atmospheric pressure. Its advantages over an elastic bandage lie in its absolute uniformity of action, a result practically impossible of accomplishment in the use of the bandage; its disadvantages in the cumbersome appliances required.

Rarefaction would be theoretically indicated in certain atrophic conditions with imperfect blood supply, dependent upon local causes, or even upon lesions in the lower segment of the cerebrospinal axis.

The abdominal or pelvic viscera can be therapeutically influenced by changes of air pressure on the lower part of the trunk, or

by the general effect of increased or diminished atmospheric density. Clinical observations are wanting to establish definite indications; and I simply make this reference as coming within the possible and legitimate scope of pneumatic therapeutics.

Having rapidly glanced at the most salient physiological effects of changes in atmospheric pressure, especially upon the organs of circulation and respiration, let us examine, as succinctly as possible, the therapeutical indications which logically and inferentially follow. Naturally diseases of the respiratory organs stand out most prominently, and in the present stage of development occupy almost the entire field. I will now briefly refer to the diseases in which pneumatic treatment is theoretically indicated and in which it has been practically tested.

Emphysema is probably entitled to the most prominent position among the diseases amenable to pneumatic treatment. Here local medication counts for little or nothing unless there is associated bronchitis; the treatment is purely mechanical. In simple vesicular emphysema we have to deal with certain abnormal physical conditions and nutritive changes. The air cells are distended by an accumulation of residual air, which the lungs, by reason of their loss of elasticity, are unable to expel. Atrophic changes occur in the alveolar walls which lead in certain areas to their obliteration and the formation of sacs of various sizes. The chest capacity becomes correspondingly increased with its altered contour.

In this disease respiration of rarefied air is theoretically indicated and has been practically justified by the most brilliant clinical results. By reducing intra-pulmonary pressure we bring to bear upon the outside of the chest wall an auxiliary expiratory force, in the relatively greater atmospheric pressure, upon the same principle that a bottle is crushed by the exhaustion of its contained air. There are few instances in practical medicine where so definite a morbid state is so completely opposed by an antagonistic mechanical procedure. Of course complete atrophy and obliteration of the alveolar walls is an irreparable physical change. But where the changes are limited to over distension a cure can be confidently expected in many cases which would be incurable by any other method. Oertel says: "The result of this pneumatic treatment is complete and permanent, the physical changes of the lungs are

entirely restored to the normal, and this form of emphysema permanently cured.”

The effect upon the circulation and nutrition is no less salutary. The anæmic tissues are liberally supplied with blood in accordance · with the physiological phenomena already described, while the general disturbances, such as edema, etc., disappear. It is certainly unfortunate that so powerful an agent in the treatment of this intractable disease should receive so little attention. Loomis, who is usually so careful a writer, loosely says that compressed air is highly esteemed in Germany in the treatment of emphysema. The fact is that in Germany the inspiration of compressed air is entirely subordinate, and alone would often aggravate, and might even produce emphysema.

Compensatory emphysema is of course irremediable by any treatment, and Oertel says that senile emphysema is equally inaccessible. Next in importance comes bronchitis, acute and chronic. Acute bronchitis of the most violent and obstinate type has been rapidly cured by Cron. My own experience in the treatment of bronchitis has been of the most gratifying character. My patients have been placed in the pneumatic cabinet with a rarefied air, and made to breathe the relatively dense air of the room variously medicated as it entered the respiratory organs. The increased intra-pulmonary pressure has an anti-hyperæmic action upon the swollen and congested mucous lining, pressing the blood out much as an elastic bandage presses the blood from the veins of the leg. This effect is readily seen in the visible membranes of the mouth and throat, as I have repeatedly observed. The excessive secretion which is dependent upon the enormous blood supply is rapidly checked, and the course of the bronchitis cut short. A not very limited experience has fully convinced me that the course of bronchitis can be greatly shortened by pneumatic treatment, while chronic and incurable cases can be greatly benefited.

The pneumatic treatment of idiopathic asthma is much less satisfactory. We are not able, with our present knowledge, to lay down specific indications. Perhaps a more complete understanding of its pathology will aid us in this direction. The inspiration of

'Respiratory Therapeutics, p. 538.

compressed air during a paroxysm would seem to be theoretically indicated to counteract the bronchial spasm. Clinical experience, however, does not seem to sustain this theoretical deduction. When compressed air is beneficial, as it often is, it would seem to be rather by its mechanical effect upon the swollen mucous lining then by opposing bronchial spasm.

Of more decided benefit is expiration into rarefied air in the intervals between the attacks, alternating with inspiration of compressed air. Besides antagonizing the tendency to the development of emphysema, which exists in this disease, this method of treatment lessens the severity and frequency of the spasmodic attacks. A complete cure of idiopathic asthma can not be confidently predicted in any given case; but it should be carefully tried in all cases which do not yield to other treatment.

In effusions within the pleural sac pneumatic therapeutics find a legitimate object of attention. When the effusion is serous its absorption can be aided by increasing intra-pulmonary pressure by the respiration of compressed air. The sac of effused liquid is compressed between the distended lung and the chest wall with a force which promotes absorption just as a bandage promotes absorption of serous effusion from the intercellular spaces of a limb. Clinical experience has fully sustained these deductions.

A further indication in these cases is the expansion of the compressed lung. Even when absorption does take place, the lung, as is well known, may fail to expand; especially if it has been compressed too long. The timely use of compressed air may save the lung from permanent consolidation as a result of too long continued compression. Where the effusion is purulent, of course the idea of mechanical treatment for the purpose of promoting absorption is not to be entertained. But if thoracentesis has been practiced, the effusion being either serous or purulent, the consentaneous action of compressed air will favor a more rapid and complete evacuation of the plural sac, while its further employment will modify the secretory process and favor a cure by adhesion.

In the treatment of phthisis the most important and satisfactory application of pneumatic therapeutics lies in the domain of prophylaxis. If the habit or diathesis which so frequently results in phthisis could receive appropriate pneumatic as well as hygienic,

dietetic and sanitary treatment I am fully convinced that the death rate from comsumption could be very materially reduced. Compressed air should be used in these cases for a long time in order to expand the lungs and improve their circulation and nutrition. When preventive medicine receives due recognition the pneumatic treatment of the phthisical habit will become a common, as it is now a recognized procedure. In those apical catarrhs which, when localized, are always, according to Rindfleisch, associated with tubercle, Oertel says that pneumatic treatment will do more than all other treatments combined. In confirmed phthisis much may still be done. In its incipient stage many cases can be cured. Increased pulmonary pressure by the processes already described improves the nutrition in the peritubercular zone. It may and often does, as I have repeatedly observed, produce the absorption of the inflammatory products which accompany and surround the tubercular process. In conjunction with other measures of a general character it may bring about the conditions which result in arrest, and which always may be equivalent to cure. In the more advanced cases much may still be accomplished. Combined with antispetic local medication I have seen cough and expectoration diminished, appetite and nutrition improved, and in some cases apparent cure result. My experience in this direction has been in part recorded in a paper read before the Fort Wayne Academy of Medicine, and published in the Boston Medical and Surgical Journal, for April 14, 1887. Inspired by the knowledge of the fact that even advanced phthisis can be cured, we should make ceaseless endeavor to promote those conditions, both local and general, which experience and reason teach us will favor this end.

Respiratory insufficiency from various causes, requires notice in this connection. In certain cases of stenoses of the respiratory tract, atmospheric pressure may be utilized to secure a more perfect ingress or egress of air. In conditions, also, of muscular debility pneumatic treatment may supplement muscular action and bring about improved hematosis, which, reacting upon general nutrition and muscular strength, will soon enable the patient to fill the lungs without the aid so rendered.

In the treatment of heart disease the indications are not, as yet, well defined. The physiological effects upon the circulation show