204 ACTION OF DIMINISHED ATMOSPHERIC PRESSURE. 



of the action of the pressure of the atmospheric pressure upon large masses, take 

 that brought about by the adhesion of the smooth, sticky, moist, articular surfaces 

 of the shoulder and hip joints ; the arm and the leg are supported without the 

 action of muscles. The thigh-bone remains in its socket after section of all the 

 muscles and its capsule. Even when the cotyloid cavity is perforated, the head of 

 the femur does not fall out of its socket. The ordinary barometric variations affect 

 the respiration a rise of the barometric pressure excites, while a fall diminishes, 

 the respirations. The absolute amount of C0. 2 remains the same ( 127, 8). 



Great diminution of the atmospheric pressure, such as occurs in ballooning (highest ascent, 

 8600 metres), or in ascending mountains, causes a series of characteristic phenomena : (1) In 

 consequence of the diminution of the pressure upon the parts directly in contact with the air, 

 they become greatly congested, hence there is redness and swelling of the skin and free mucous 

 membranes ; there may be haemorrhage from the nose, lungs, gums ; turgidity of the cutaneous 

 veins ; copious secretion of sweat ; great secretion of mucus. (2^ A feeling of weight in the 

 limbs, a pressing outwards of the tympanic membrane (until the tension is equilibrated by 

 opening the Eustachian tube), and as a consequence noises in the ears and difficulty of hearing. 

 (3) In consequence of the diminished tension of the O in the air ( 129), there is difficulty of 

 breathing, pain in the chest, whereby the respirations (and pulse) become more rapid, deeper, 

 and irregular. When the atmospheric pressure is diminished -, the amount of in the blood 

 is diminished, the C0 2 is imperfectly removed from the blood, and in consequence there is 

 diminished oxidation within the body. When the atmospheric pressure is diminished to one- 

 half, the amount of C0 2 in arterial blood is lessened ; and the amount of N diminishes pro- 

 portionally with the decrease of the atmospheric pressure. The diminished tension of the air 

 prevents the vibrations of the vocal cords from occurring so forcibly, and hence the voice is feeble. 

 (5) In consequence of the amount of blood in the skin, the internal organs are relatively ansemic ; 

 hence, there is diminished secretion of urine, muscular weakness, disturbances of digestion, 

 dulness of the senses, and it may be unconsciousness, and all these phenomena are intensified by 

 the conditions mentioned under (3). Some of these phenomena are modified by usage. The 

 highest limit at which a man may still retain his senses is placed by Tissandier at an elevation 

 of 8000 metres (280 mm. Hg). In dogs the blood-pressure falls, and the pulse becomes small 

 and diminished in frequency, when the atmospheric pressure falls to 200 mm. Hg. 



Those who live upon high mountains suffer from a disease " mal de montagne," which consists 

 essentially in the above symptoms, although it is sometimes complicated with ansemia of the 

 internal organs. Al. v. Humboldt found that in those who lived on the Andes the thorax was 

 capacious. At 6000 to 8000 feet above sea-level, water contains only one-third of the absorbed 

 gases, so that fishes cannot live in it. Animals may be subjected to a further diminution of the 

 atmospheric pressure by being placed under the receiver of an air-pump. Birds die when the 

 pressure is reduced to 120 mm. Hg ; mammals at 40 mm. Hg ; frogs endure repeated evacua- 

 tions of the receiver, whereby they are much distended, owing to the escape of gases and water, 

 but after the entrance of air they become greatly compressed. The cause of death in mammals 

 is ascribed by Hoppe-Seyler to the evolution of bubbles of gas in the blood ; these bubbles stop 

 up the capillaries, and the circulation is arrested. Local diminulion of the atmospheric pressure 

 causes marked congestion and swelling of the part, as occurs when a cupping-glass is used. 



Great increase of the atmospheric pressure causes phenomena, for the most part, the reverse 

 of the foregoing, as in pneumatic cabinets and in diving-bells, where men may work even under 

 4 atmospheres pressure. (1) Paleness and dryness of the external surfaces, collapse of the 

 cutaneous veins, diminution of perspiration, and mucous secretions. (2) The tympanic mem- 

 brane is pressed inwards (until the air escapes through the Eustachian tube, after causing a 

 sharp sound), acute sounds are heard, pain in the ears, and difficulty of hearing. (3) A feeling 

 of lightness and freshness during respiration, the respiration becomes slower (by 2-4 per minute), 

 inspiration easier and shorter, expiration lengthened, the pause distinct. The capacity of the 

 lungs increases, owing to the freer movement of the diaphragm, in consequence of the diminu- 

 tion of the intestinal gases. Owing to the more rapid oxidations in the body, muscular move- 

 ment is easier and more active. The O absorbed and the C0 2 excreted are increased. The 

 venous blood is reddened. (4) Difficulty of speaking, alteration of the tone of the voice, 

 inability to whistle. (5) Increase of the urinary secretion, more muscular energy, more rapid 

 metabolism, increased appetite, subjective feeling of warmth, pulse beats slower, and pulse-curve 

 is lower (compare 74). In animals subjected to excessively high atmospheric pressure, P. Bert 

 found that the arterial blood contained 30 vols, per cent O (at 760 mm. Hg) ; when the 

 amount rose to 35 vol. per cent, death occurred with convulsions. Compressed air has been 

 used for therapeutical purposes, but in doing so a too rapid increase of the pressure is to be 

 avoided. Waldenburg has constructed such an apparatus, which may be used for the respira- 

 tion of air under a greater or less pressure. 



Frogs, when placed in compressed O (at 14 atmospheres), exhibit the same phenomena as if 



