ure, affects both and equally the respired and the surrounding atmosphere. A differential change affects one of these factors only, or both unequally. Differentiation may be made to (directly) affect inspiration only, or expiration only; or it may be made to affect both phases of respiration, equally or unequally, in the same or in opposing directions.

While it is true, that patients may by change of residence to a more or a less elevated region, be subjected to absolute change in atmospheric pressure, yet this is, after all, but one of the factors in climato-therapy, and a brief allusion to the fact is all that properly falls within the scope of the present paper.

The absolute method in pneumato-therapy is applied by means of apparatus termed pneumatic chambers; a number of which have been constructed and are in use at different points in Continental Europe, but I am not aware of any establishment of the kind in English-speaking countries. The first of these was made, after designs by Tabarie, in 1838. The literature of the subject, however, is much older,* Tabarie having made his first communication to the Academy of Sciences at Paris in 1832, and Jounod having presented his first paper in 1835; while even in the eighteenth century, the attention of naturalists had been directed to the effects of condensed air on animal and vegetable life. Tabarie's cabinet could be used only with compressed air. G. Lange modified the apparatus so that rarefied air might also be employed, and so that expiration, if so desired, might be made directly into the outer atmosphere. In this latter respect, we find the first attempt at differentiation. It was in Lange's cabinet that Von Vivenot prosecuted his valuable and laborious researches. Von Liebig designed for the Mack Brothers at Reichenhall a pneumatic chamber said to be the best in existence, while that of Simonoff at St. Petersburg, consisting of a stone chamber and two iron ones, is said to be the most elegant in its appointments. The patient, or a number of patients, having entered one of these appliances, the contained air is then gradually condensed or rarefied by means of a steam-pump; the pressure being gradually restored to the normal after a sitting of from half an hour to two hours or

*For hi-torical and bibliographical details, see J. Solis-Cohen, "Inhalation: its Therapeutics and Practice," second edition, Philadelphia, 1876; Oertel, "Handbuch der Respiratorischen Therapie," Leipzig, 1882. English translation by J. Burney Yeo, London, 1885.

longer. Special appliances secure proper ventilation, and permit regulation of pressure, of temperature, etc. These chambers are very costly, and their use necessarily restricted to certain resorts. stricted to certain resorts. Hence, for a long while, various attempts have been made to construct cheaper and portable apparatus. The portable apparatus utilize the differential method, that is to say, the air within the lungs is rendered different in pressure from the surrounding atmosphere.

Changes of intra-thoracic air-pressure can of course be obtained without any apparatus whatever. Thus, if, while nostrils and mouth are closed, forced expansion of the chest be made (Mülier's experiment), the air within. the lungs will be rarefied; and conversely, if, after a full inspiration, the glottis, or the mouth and nostrils, be closed, and an effort made to contract the chest (Valsalva's experiment), assisted, perhaps, by manual compression (Weber's experiment), the intra pulmonary air will be condensed. A less degree of condensation may be caused by expiring through but partially-closed lips; and a simple contrivance based upon this principle-a narrow tube, with a ball-valve to resist expiration -produces the same effects as expiration into compressed air. It is obvious, however, that the effect of rarefaction can thus be obtained only during a prolongation of the inspiratory phase of the respiratory act, while compression can be brought about only by a baffled or impeded expiration. The respiratory rhythm is completely deranged, the mechanical force employed and developed remains an unknown and variable quantity, while the disturbance of circulation is usually out of all proportion. to the therapeutic value of the expedients.

Resort to apparatus for furnishing a supply of condensed or rarefied air is therefore preferable. Simple matter as the construction of such apparatus should seem to be, it was not until 1870 that any practical device at all fulfilling the necessary conditions was made; and not until 1874 that a reliable apparatus was presented to the profession. To Hauke, of Vienna, belongs the credit of having made the first approach to a suitable instrument; and to Waldenburg, of Berlin, is due the honor of having constructed an apparatus which has served as the model of the best of subsequent ones, and of having placed pneumato-therapy upon a firm scientific basis, by patient and accurate physiological and clinical studies.t

In the arrangement of apparatus for the therapeutic use of compressed and rarefied air, two desiderata must be secured with mathematical precision,-1. The pressure must be a known and controllable quantity; 2. It must be constant, or varied only at will. The physical principles involved, are identical with those involved in a study of the physiological effects of pneumato-therapy; depending upon the properties of the gaseous state of matter, the tendency of matter in whatever state to move in the direction of least resistance, and the fact that the effect of terrestrial gravity upon the atmosphere, is to subject everything upon the surface of the earth to a continuous pressure, which, measured at sea-level, is represented by the weight of a column of mercury 760 mm. (29.9 inches) high,-.e., in round numbers, fifteen pounds to the square inch.

Two classes of apparatus have been constructed for the utilization of differential pressure. In the one, the air is condensed or rarefied in a receptacle from which the patient inspires, or into which he expires; in the other, the patient is placed within a contrivance in which the air surrounding his body, or a portion of his body, may be condensed or rarefied, while he breathes the ordinary atmosphere. Instruments of both classes were first constructed by Hauke.

We will consider first the most useful class, that in which the patient remains outside the apparatus.

Pressure or rarefaction may be obtained on one of three plans, which may be termed the water-level plan, the gasometer plan, and the bellows plan. The water-level plan depends upon the fact that change of waterlevel, without entrance or exit of air, in a vessel containing both air and water, will alter the density of the air. This was the principle first adopted by Hauke, and subsequently by Stoerk. Apparatus constructed on this plan simply, are not reliable, and are inconstant. The bellows plan depends upon the fact that a receptacle, with extensible and collapsible walls, may be made by expansion of the cavity to rarefy the contained air, and by contraction to condense it. The lungs work in this manner. The best apparatus for pneumatotherapy constructed on this principle is that of Biedert; one of the simplest and cheapest that of B. Fraenkel. While they are said to have answered admirably, they evidently can easily become fouled if used for expiration, and the pressure does not remain constant. Biedert's is also troublesome to manage. The

principle is simple, however, and means for its employment readily available. Thus, J. Solis-Cohen, in 1866,* used a kitchen bellows to administer inspirations of condensed air, and the same writer in 1880† highly recommended a simple expedient to secure compression, suggested by Dr. W. Y. Gadberry, of Yazoo City, Mississippi,-namely, the employment, after deep inspiration, of an ordinary rubber hand-ball to force an additional quantity of air into the lungs,—as being more useful than drugs in promoting expectoration.

The gasometer plan depends upon the fact that if a vessel open at bottom, and with an opening at top to admit air, which may be closed when desired,-being suspended over water in another vessel, freely communicating with the outer air,-be raised out of the water by a force sufficient to overcome gravity and atmospheric pressure, the air will rush into its interior; that if the cylinder be then closed, the contained air may be rarefied or condensed by adding or subtracting gravity, or its equivalent, to or from atmospheric pressure; and that the positive or negative pressure thus obtained is independent of the volume of air within the air-chamber, which will rise or fall within the water accordingly. Thus we have a ready means of obtaining any desired pressure and of maintaining it, whether we withdraw air by inspiration, or add air by expiration. This is the principle upon which Waldenburg's apparatus is constructed, and upon which depend the modifications of Schnitzler, Weil, Tobold, Finkler and Kochs, and others, all admirable instruments and thoroughly reliable. The best of these are expensive. The minor objections to all instruments of this class are that they are more or less cumbersome, are troublesome to manage, and are not continuously acting, the capacity of the cylinder being of course limited.

This latter objection has been overcome in various ways. Some have so combined two cylinders that one rises while the other falls, and vice versa, permitting the patient to use one or the other alternately, with but slight interruption to the process. Geigel and Mayr, whose instrument Oertel commends above all others, have combined a water-level instrument (water-engine bellows) with a gasometer-bell; a series of revolving buckets taking up or discharging a certain quantity

* Op. cit., p. 55.

†Trans. Med. Soc. of Penna., Phila., 1880.

of water to compress or rarefy the contained air, which passes into the bell. This instrument is very costly. The continuous action, which is its great merit, can be secured in a much simpler and cheaper manner, by combining a foot-bellows, such as is used by dentists, with a Waldenburg or other gasometer. This is practically the plan of the instrument which, with the assistance of Mr. Chas. Richardson, I devised in 1883, and which I have already described and exhibited to this society. Originally intended, only to furnish to patients a cheap and safe instrument for home use with compressed air, I have found it capable of modification in other directions; so that when Mr. Richardson has concluded some experiments which he has kindly undertaken to test the feasibility of plans submitted to him, I hope to be able to present to the society an improved instrument, but slightly advanced in cost, which may be used for all the purposes to which the more expensive instruments are applied. Scales and gauges for exact research, may of course be attached to this, as to any other apparatus. To all of the forms of apparatus mentioned, except the simple accordion of Fraenkel, attachments may be added for warming, chilling, drying, moistening, or medicating* the air. Whatever plan be adopted, separate instruments should be used for expiration and inspiration; or two cylinders or bells may be combined in one instrument, as in the "double ventilators" of Waldenburg, Weil, Schnitzler, and Geigel and Mayr. Each patient should have his own mask or mouth-piece.

In order to obtain condensation or rarefaction of the atmosphere surrounding the chest, or the body, of patients unable, or, as in the case of children, unwilling, to undergo treatment by methods requiring their more or less active co-operation, Hauke has devised two forms of apparatus. In one, the chest only is surrounded by an air-tight cuirass, the air between which and the thoracic walls is either condensed or rarefied, the patient respiring the ordinary atmosphere. In the other form, the trunk and limbs enter the apparatus, the face alone being free. A very elegant but more elaborate and expensive means of arriving at the same result, is the pneumatic

* My own usual practice is to pass the air through a Wolff bottle containing a volatile medicament, suspended or dissolved in water, or floating upon the surface of the water. Creasote, terebene, thymol, iodine, benzoin, and similar substances may be thus employed. There are many other ways of medicating the respired air, but this subject is not properly within present limits.

cabinet devised by Mr. Ketchum, of Brooklyn, and introduced to the profession by Dr. H. F. Williams of that city. The patient sits in an air-tight cabinet, the air about him being condensed or rarefied, while he respires the ordinary air, which is conducted to his mouth from the outside, by tubing. The respired air is charged with sprays of certain sub

stances.

Were it not for the undemonstrable and misleading claims put forth by the proprietors of this patented instrument, and the questionable propriety of the methods by which it has been placed upon the market, I might pass it with this simple allusion. But since certain claims of historical novelty have misled even so accurate a student as my friend Dr. Platt, of Lakewood, who has completely disproved claims of scientific novelty and unscientific mystery, I cannot complete this portion of the present article without a plain-spoken denial of these claims. That the instrument is not new in mechanical principle-whatever novelty and merits it may have in mechanical details, from which I have no desire to detract-is proved by the simple reference to the pneumatic chamber of Lange, and the pneumatic cuirass and pneumatic tub of Hauke. That it is not new in therapeutic principle goes almost without saying; for since differentiation of intra-thoracic from extra-thoracic pressure is the sole object, of what moment can it be, whether this differentiation be obtained by raising the one, or by lowering the other? Until those who claim superior virtues for the pneumatic cabinet can prove that the difference between 29 and 30 is either greater or less than the difference between 30 and 31, they will scarcely find general acceptance of their proposition.

That the cabinet offers a convenient and elegant method of applying some of the wellknown principles of pneumato-therapy, none can deny. Those who prefer it to other and simpler means of accomplishing the same end, are justly entitled to use and express the preference. I simply wish to place on record a flat denial of the assertions that there is any therapeutic novelty about it; or that anything whatever can be done with it, that cannot be done at least equally well, and, in some instances, better, with Waldenburg's, Schnitzler's, or Geigel and Mayr's instrument; or that

N. Y. Medical Journal, Nov. 6 and 13, 1886.

The questions as to penetration of sprays and vapors are not now under consideration. Dr. Platt's article will elucidate this matter.

the results obtained by its use are any better than those obtained for nearly fifty years in Europe, and for at least ten years in America, with the various methods of pneumatotherapy, which I have described this evening.

This will be made clearer as we now pass to the consideration of the mechanical effects of compressed and rarefied air upon circulation and respiration. I say mechanical effects, for these are calculable and measurable with mathematical exactitude. That there must result as well certain other effects, through the nervous system especially, hardly admits of doubt; but the evidence is not perfectly clear and uncontradicted, and the explanation of observed facts is yet involved in obscurity. Not so, however, with the effects due solely to pressure, which follow the same rules as pressure-effects outside the body.*

Let us first review briefly, the well-known mechanism of respiration and of circulation. When by the expansion of the thorax, the contained air is rarefied, the denser outer air tends inward; when the thorax contracts, it compresses the contained air, which tends outward to the now rarer atmosphere. The amount of normal differentiation is small, having been estimated, from observations made in cases of wounds of the trachea, at — 1 mm. Hg. during inspiration, and + 2 to 3 mm. Hg. during expiration. Forced inspiration, however, gives a negative pressure averaging 57 mm. Hg., while forced expiration gives a positive pressure averaging 87 mm. Hg.

The average volume of air which enters or leaves the chest during inspiration or expiration, the tidal air, is small, having been estimated at twenty cubic inches; but on forced inspiration this can be increased by one hundred and ten cubic inches of complemental air; while forced expiration can expel one hundred cubic inches additional, properly termed the reserve air, improperly, the residual air; leaving still in the chest one hundred cubic inches of residual air or stationary air. The term residual air, as used in this paper, refers to the latter quantity. The object of this movement of air, is to introduce into the blood O, and to remove from it CO,. This is accomplished in the alveoli; the air of

*For physiological data and references, see Landois's "Physiology," translated and edited by Stirling. For the physical principles, consult Ganot's or other standard works on "Physics." For elaborate studies, see Waldenburg's and Oertel's works cited. The latter gives full references to investigations up to the date of publication (1882).

which is consequently continually richer in the latter gas, and poorer in the former, than the air of other portions of the lungs; there being by diffusion a gradual increase of one and diminution of the other, until we reach the trachea and larger bronchi, in which the air most nearly corresponds to the outer atmosphere. mosphere. At each inspiration there is an absolute as well as a percentage gain of O and percentage loss of CO,; at each expiration there is an absolute loss of both, without percentage change from the end of inspiration, except as effected by the gaseous movement within the alveoli. This movement is in part due to the relatively higher tension of O in the alveolar space, and of CO, in the blood, the former passing inward, the latter outward. The volume of O which can be absorbed by the blood is the same at all pressures, but as the weight of a given volume increases with its density, the weight of gas absorbed increases with the pressure. The combination of O with the hæmoglobin, and the liberation of CO, from the salts of the plasma, depend largely upon the partial pressure of these gases; association being favored by high partial pressure, dissociation by low partial pressure. Now, both tension and partial pressure, while necessarily depending upon actual pressure, also depend directly upon relative volume, other things being equal. Consequently, whatever tends to increase the relative volume and actual pressure of O in the alveoli, within certain limits, facilitates both its passage into the blood and its association with the hæmoglobin; and whatever tends to diminish the relative volume of CO, in the alveoli, within similar limits, facilitates its dissociation from the salts and its escape from the blood.

Whatever increases pulmonary ventilation —that is, the volume of air taken in and expelled during each act of respiration-manifestly increases the pulmonary supply of O, and diminishes the quantity of CO,; and pulmonary ventilation will be facilitated in one respect by an increase in the negative pressure of inspiration, and in the other, by an increase in the positive pressure of expiration. The weight of O in any given volume of air, and consequently in any given. volume of O absorbed into the liquid blood, is of course increased directly as the pressure. Any process that would, while increasing the weight of O absorbed, also increase the rapidity and volume of the pulmonary circulation, would thereby bring a greater number of corpuscles into contact with the greater