276 ACTION OP DIMINISHED ATMOSPHERIC PRESSURE. 



The solids consist of elementary parts (cells and fibres), each of which 

 presents only a microscopic surface to the pressure, so that for each cell 

 the prevailing pressure of the air can only be calculated at a few 

 millimetres a pressure under which the most delicate histological 

 tissues undergo development. As an example 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. In these cases, 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 (Brothers' Weber). Even when the colytoid cavity is perforated, 

 the limb 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). 



A Great Diminution of the Atmospheric Pressure, such as occurs in 



ballooning (highest ascent, 8,600 meters), 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 of 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 (Bert, Friinkel and Geppert), the COo is imperfectly re- 

 moved 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 proportionally 

 with the decrease of the atmospheric pressure (Frankeland Gepert). 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 anremic ; hence, there is 

 diminished secretion of urine, muscular weakness, disturbances of digestion, dull- 

 ness 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 8,000 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 com- 

 plicated with anajmia of the internal organs. Al. v. Humboldt found that in those 

 who lived on the Andes, the thorax was capacious. At 6,000 to 8,000 feet above 

 sea-level, water contains only one-third of the absorbed gases, so that fishes cannot 

 live in it (Boussingault). Animals may be subjected to a farther diminution of the 

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



