As a general rule, the sick require more air-space than the healthy. The mere cubic dimensions are much less important than the amount of oxygen available for respiration; but as the sick are more readily affected by draughts than the healthy, it follows that the sick require more cubic space, and less frequent renewal of the air. It seems generally conceded that 2,000 cubic feet of air-space per patient is necessary in hospitals and in the sick-room to supply the needed amount of oxygen, although a less space may be better if provided with the means of frequent changes of air without sudden variations of temperature and strong currents. A large cubic space of stagnant air will be inadequate to the requirements of the sick. Even when so large an amount of air as 3,700 cubic feet per hour for each patient has been supplied to a hospital ward, the air in it has had a distinctly "stuffy" and offensive smell. Everybody is familiar with the fact that the sick and wounded do better in tents and in the open air, than in the best constructed military hospitals.

If, as has been affirmed by the highest sanitary authorities, 1,000 cubic feet of air-space is necessary to a healthy adult, it is clear that the sick require not less than we have named, 2,000; for the renewal of the air in the case of the latter must be less rapid. As the means for the renewal of the air in the sick-chamber in private houses consist of doors, windows, and fireplaces—or natural ventilation—the supply to the patient is variable. To insure the best results under these circumstances, the bed should be so placed as to be without stagnant corners and recesses, and yet not within the range of currents or draughts. When the air is still, movements may be produced by burning a lamp in the chimney. In cold weather the fire in the fireplace induces a strong upward current in the chimney, the air coming from all the crevices. It would be quite beyond the subject-matter of this treatise to consider the various mechanical contrivances which have been proposed, and are now used, to secure proper ventilation in public institutions and hospitals; but it may be useful to mention those devices by which natural ventilation in the sick-chamber may be promoted.

Where there are opposite windows, cross-draughts may be prevented by the following expedients: 1, by giving an upward slope to the window so that the current of fresh air is deflected toward the ceiling; 2, by having some of the window-panes doubled, the outer one having a space at the bottom of the pane, and the inner one at the top; 3, by fastening a block to the upper sash which prevents closing. If there are windows at one side only, the room may be efficiently ventilated by vertical tubes carried up the walls from some distance (a few feet) and communicating with the external air.

In the fevers, exanthemata, diphtheria, dysentery, etc., an abundant supply of air is a measure of the highest utility. The result in a doubtful case may be determined by the amount of oxygen received by the patient. Furthermore, free admission and exit of air is the most efficient means of destroying disease-germs, and their retention in a stagnant atmosphere intensifies their virulence. In febrile affections, the apprehension of "taking cold" may be allayed by the assurance that the condition of fever is preventive. Draughts, however, should be avoided in measles and in all affections of the breathing organs.

There are two conditions in diseases of the respiratory organs, in which an abundant supply of air is essential: inflammatory affections in which the breathing space is encroached upon so that the oxygenation of the blood is hindered; and chronic maladies, as emphysema, asthma, etc., in which labored breathing is a consequence in part of mechanical defects. Considerable diminution in the supply of air has a powerful influence in the production of consumption. The statistics on this point collected by the English Sanitary Commission seem conclusive, and, since their recommendation of increased cubic air-space in the barracks, the number of cases of phthisis has materially diminished. In the treatment of this disease, a suitable supply of air becomes even more imperative. The subjects of this disease should occupy apartments, whenever practicable, provided with ample windows and fireplace, and frequent renewal of the air day and night should be secured by some of the contrivances now used for this purpose and already referred to. Whenever, by reason of fever or debility, exercise in the open air can not be taken, the patient, suitably clad and protected in severe weather, may sit in an apartment with all the windows and doors open, a part of each day.

Maladies characterized by a deficiency in the oxidation processes throughout the body require increased supply of air under all the circumstances of life. The most important of these are diabetes, gout, rheumatism, obesity, excess in the production of lithates, etc. The good effects of open-air exercise in these disorders result chiefly from the increased consumption of oxygen. Anaemia, chlorosis, convales-cence from acute diseases, and chronic wasting maladies, also require increased consumption of air: the oxygen is even more important than the iron which is given so profusely in these cases; indeed, without additional oxygen, the assimilation of the iron can hardly be accomplished.

Therapeutical Applications of Compressed Air are effected by two modes: by placing the patient in a chamber in which the air has been condensed by an air-pumping engine; and by having the patient breathe, through a mask closely fitting the mouth and nose, air compressed in a portable reservoir. The latter method only is ordinarily available. Without entering into minute details, it will suffice to say that the former method consists of an air-tight chamber eight feet high and seven feet wide, in which three patients can sit comfortably. The air is compressed gradually to one and a half atmospheres —a pressure of twenty-two pounds to the square inch—and the patient remains in the chamber about an hour and a half. One of the first and most complete arrangements of this kind was erected under the supervision of Dr. Liebig (not the chemist) at Reichenhall, Bavaria; and he has since communicated the results of his large experience to the Aerztliches Intelligenz-Blatt of Munich. The portable apparatus now most used is that of Waldenburg (der transportable pneumatische Apparat). This consists of an outer cylinder containing some water, and an inverted inner cylinder containing air, which fits into the outer one. Obviously the air within may be condensed or rarefied by lowering or raising the inner cylinder, which is easily effected by applying weights. A mercurial manometer indicates the degree of condensation, and a water-gauge the height of the water. With the air-chamber a flexible tube, having an oro-nasal mask attached, communicates. With this apparatus the patient breathes either condensed or rarefied air at the will of the operator. The author has had arranged for his own use a pneumatic apparatus which can be employed for inhalation of compressed or rarefied air, and for the atomization of liquids. It is only available in cities where a sufficient water-pressure can be obtained. It consists of a brass cylinder strongly made, and containing at the top a stop-cock and pipe for the admission of water, and at the bottom a stop-cock for drawing off the water. At the top, also, there is a stop-cock and pipe for the attachment of the flexible tube and oro-nasal mask, and a gauge for registering the pressure. The admission of water effects the compression of the air; its removal—all the stop-cocks being closed—effects the rarefaction. Precisely the same results can be attained as in the more complicated arrangement of Waldenburg. Furthermore the author's apparatus can be employed as an atomizer, using compressed air or steam.

The applications of compressed air are numerous and important The results are chemical and mechanical. The chemical effects are due to the increased supply of oxygen; the mechanical, to the distribution of the blood-pressure. In anaemia, chlorosis, amenorrhoea, in the neuralgiae, especially of the fifth nerve, headache, epistaxis, in gout, diabetes, obesity, etc., very excellent results are obtained by the use of compressed air—which means the increased consumption of oxygen. To achieve all that is possible to effect in these cases, the treatment must be continued for a considerable time.

It is, however, in certain cardiac and pulmonary affections that the pneumatic treatment is especially commended. Acute catarrh, nasal, faucial, bronchial, if early applied; chronic bronchitis, with or without emphysema, capillary bronchitis, atelectasis, asthma, dilatation of the right cavities, and fullness of the venous with ischaemia of the arterial system, are conditions in which the compressed air is signally beneficial. Probably in emphysema, more than in any other malady, has the relief afforded by this treatment been most conspicuous; for this is a disease which has hitherto offered few results to therapeutical skill. "Die Exspiration in verdünnter Luft ist das specifische mecha-nische Antidot des Emphysems," is the dogmatic statement of Walden-burg—" Expiration into rarefied air is the specific mechanical antidote to the emphysematous affections."

The rules for the inspiration and expiration of rarefied and condensed air respectively may be formulated as follows:

As inspiration of condensed air increases the intra-thoracic air-pressure, it impedes the flow of blood to the right auricle, and lessens somewhat the pulse-rate, and is accordingly indicated in cases of dyspnoea having a mechanical origin, in incipient phthisis, in asthma, bronchitis, and in insufficiency of the mitral.

As inspiration of rarefied air has the opposite effects to those of condensed air, its use is indicated in the few cases in which increased inspiratory power is desirable, as in contracted thorax, the result of effusion.

Expiration into condensed air increases the expiratory power when deficient, and expiration into rarefied air is indicated in emphysema and chronic bronchitis.