252 EFFECTS OF ATMOSPHERIC PRESSURE. 



vailing pressure that is, the partial pressure of the several gases and 

 also with their temperature. The solid constituents of the body are 

 composed of innumerable and minute elementary parts, such as cells 

 and fibers, of which each presents only a microscopic extent of surface 

 to the influence of the pressure. Hence, the prevailing atmospheric 

 pressure for every cell can be estimated only at a few milligrams, a 

 pressure under which even the most delicate histological structures 

 develop with ease. As an example of the action of atmospheric pressure 

 on larger masses, attention may be called to the fact that, as a result 

 of the adhesion of the smooth, sticky, articular surfaces of the shoulder- 

 joints and the hip-joints, the arm and the thigh are supported without 

 the aid of muscular activity; so that, for example, the thigh is still held 

 in^ the acetabulum after all of the soft parts around the neck of the femur, 

 including the articular capsule, are divided. 



An ordinary increase in barometric pressure has an influence on 

 the respiratory activity in that it stimulates slightly the respiratory 

 movements, while a fall in barometric-pressure has the opposite 

 effect. The absolute amount of carbon dioxid remains the same; but 

 in connection with the lessened frequency of respiration attending a 

 low barometer, the percentage is naturally somewhat increased. 



Marked diminution in the atmospheric pressure, such as occurs in ascending 

 mountains or in balloon-voyages (the highest known ascension, without loss of con- 

 sciousness having been made by Berson of Berlin, to a height of 9145 meters at 

 a temperature of 47.7 C.), causes a series of characteristic phenomena: (i) As 

 a result of great diminution in the pressure on surfaces in direct contact with the 

 air, they undergo marked congestion. Hence, there occur redness and swelling 

 of the skin and exposed mucous membranes, even to the extent of causing hemor- 

 rhages from the more delicate parts, as the nose, the lungs, the gums; turgidity of 

 the cutaneous veins, profuse sweating, marked secretion from the mucous mem- 

 branes. The arteries become more empty; at one-half the atmospheric pressure 

 the blood-pressure in the radial artery begins to fall. (2) Other direct effects 

 of diminished pressure are a feeling of weight in the legs, as the atmospheric pres- 

 sure alone is not sufficient to keep the head of the femur in the acetabulum ; bulg- 

 ing of the tympanic membrane by the air in the tympanic cavity, until the differ- 

 ence in tension is equalized through the Eustachian tube, and as a 'consequence 

 pain in the ears and even impairment of hearing. (3) The diminution in the 

 tension of oxygen in the surrounding air causes difficulty in breathing and oppres- 

 sion of the chest, as a result of which the respirations become more rapid (also 

 the pulse), deeper, and irregular. At an elevation of from 3000 to 4000 meters 

 the respiration and pulse are increased one-fourth ; when the atmospheric pressure 

 is reduced from one-third to one-half, the blood loses oxygen, and in consequence 

 there is incomplete removal of the carbon dioxid from the blood and a considerable 

 diminution in the oxidation-processes in the body. When the atmospheric pres- 

 sure is one-half or less, the amount of carbon dioxid in the arterial blood is dimin- 

 ished, and the amount of nitrogen decreases in proportion to the diminution in 

 atmospheric pressure. Rabbits kept under a pressure of from 300 to 400 mm. of 

 mercury die on the third day, and present widespread fatty degeneration, espe- 

 cially of the heart. 



In men and in animals, residence in high, mountainous regions appears to 

 increase in the course of a few days the amount of hemoglobin in the blood and 

 the number of red corpuscles. This effect should be favorable for the absorption 

 of oxygen. A noteworthy phenomenon is the appearance of numerous microcytes 

 in the first few days. Dyspnea from various causes also has a similar effect in 

 man. (4) In consequence of the diminution in the density of the air, the latter 

 is not able to produce loud tones in the larynx through the vibrations of the vocal 

 bands; hence, the voice appears faint and altered. (5) In consequence of the 

 determination of blood to the external parts in contact with the air, the internal 

 parts become relatively poor in blood ; hence result diminution in the secretion of 

 urine, muscular weakness, digestive disturbances, dulness of the senses, fainting 

 spells, all of which phenomena are intensified by the conditions mentioned in 



