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226 CHAPTER 13 1948 Guide cabinet during the induction phase. . When the desired body temperature has been reached by electrical induction, the atmosphere of the enclosure js kept at saturation to prevent heat loss, thus maintaining the patient's temperature at the desired point. The two underlying principles in the production of fever by the hot, humid air cabinet are: (1) the transfer of heat by conduction from the circulating hot air to the body and (2) prevention of heat loss. The latter is more important. In an atmosphere of high humidity,, the heat loss by evaporation is markedly decreased. COLD THERAPY In contrast to fever therapy the use of cold as a means of anesthesia and treatment is of established importance. Refrigeration anesthesia is being more widely used and the advantages of the method claimed by Allen have been completely confirmed M. It has been demonstrated that the cooling of limbs and other partswith ice-water or ice, cracked or pulverized, down to near the freezing point (5 C or 40 F) is harmless. Freezing must be avoided. There is a temporary retardation or suspension of life, with resumption of cellular activity as the temperature returns to normal. A human limb can remain bloodless and anesthetic below a tourniquet for at least 8 hr and perhaps up to 48 hr without.injury, while the rest of the body remains warm. Where amputation is indicated it can thus be done without pain, loss of blood or strength and also without shock. There is no apparent interference with the subsequent healing of the stump. Refrigeration anesthesia is of importance not only in amputation but also in the control of hemorrhage, pain, infection and shock during the transportation of patients with traumatized limbs. Apart from the advantages of cold in amputations, cryotherapy has been beneficial in the treatment of burns and arterial obstruction, and essential in the treatment of frostbite and immersion foot. It has been used successfully for dental anesthesia. The principle of hibernation in which the body as a whole is cooled for as much as five days in air tem peratures between 50 to 60 F and applied to such conditions as morphine addiction, leukemia, and schizophrenia continues to be experimental. Prolonged cold therapy which keeps the body temperature below 95 F depresses the vital processes and is fraught with danger. The' methods used for refrigeration depending upon available facilities are as follows24: (1) Cracked or shaved ice which is simple and has the advantage of not freezing tissues. However, it is cumbersome and sloppy to handle and is unsuited to prolonged treatments. (2) Use of ice in a pail for immersion of local parts. (3) Special boxes for holding ice with padded or curtained openings for the limb. (4) Bare ice bags and cloth bags for iced wet dressings for prolonged treatments and convenience. (5) A double chambered cabinet using dry ice has been constructed. (6) Electrical refrigerating apparatus, consisting of a compact noiseless unit that pumps fluid to various types of applications, is available. The applicators may be in the form of blankets containing rubber tubes suitable for covering the entire body or all or part of a limb. Special applicators are available for insertion into various body cavities and for inducing dental anesthesia. (7) An air chamber at regulated temperature for treatments of frostbite and immersion foot, and amputation stumps. - Air Conditioning in the Prevention and Treatment of Disease 227 The electrical apparatus is costly but has the advantages of thermo static regulation, light weight, freedom of movement, and permits prolonged treatments with heat as well as cold over the range of tern-: peratures therapeutically desirable. ALLERGIC DISORDERS Although there is some division of opinion over the ultimate cause of allergy, the prevailing belief is that it is due to an inherited or acquired hypersensitiveness to pollen or other foreign proteins in certain indivi duals who react abnormally to the offending substance. The reaction may be induced by inhalation, eating, or absorption (through the skin) of the allergens. Some of the clinical manifestations are hay fever, asthma, eczema, and contact dermatitis. Symptoms of Hay Fever and Asthma The respiratory tract is the usual site of allergic manifestations, e.g. hay fever and asthma. In hay fever, the nose and eyes are red and itchy, and there is considerable discharge. Nasal obstruction is the most common and distressing symptom. The severity of the symptoms varies widely from day to day depending chiefly on the amount of pollen in the air. ' Seasonal asthma comes in attacks. The most popular theory concern ing the mechanism of action is that the offending substance irritates the nerve endings in mucous membranes of the respiratory tract, causing spasmodic contraction of the small bronchioles of the lungs, which interferes with breathing, particularly with expiration. Non-seasonal allergic disturbances are sometimes attributed to house or street dusts, fungi, odors, animal dander, irritating gases, and heat or cold, particu larly sudden temperature changes. It is often stated in the literature that heat regulation in asthmatic individuals tends to be unstable, with a tendency toward the subnormal. Many allergic cases who are apparently well develop their attacks when cold weather appears, or upon changing from warm to cool outdoor air. Air Conditioning Apparatus In recent years considerable effort has been directed toward the elimi nation of the principal cause of allergy from the air of enclosures by filtration or other air conditioning processes capable of removing pollens, in the hope of providing relief to individuals who fail to respond to medical treatment (desensitization or immunization). Paper or cloth filters, mounted in inexpensive' window or floor units, prove quite satisfactory in many cases, but since dust and smoke fre quently cause asthmatic attacks, it is desirable that an air filter, to be of full value in the treatment of asthma, should remove all possible dusts and pollens regardless of size or amount. Electrostatic air cleaners are more efficient than most commonly used types for capturing very fine dust. Although the chief remedial factor in the treatment by conditioned air is the filtration of pollen, a certain amount of cooling and dehumidification appears to be desirable. A comfortable temperature between 70 and 75 F and a relative humidity well below 50 per cent proved satisfactory26. Direct drafts, overcooling or overheating are apt to initiate or aggravate the symptoms.