536 THE AIR AND LIFE. 



when man rises in a balloon or c^limbs moiintaius, or betakes himself 

 to places where the pressure is naturally or artificially great, he 

 experiences certain effects which deserve some mention. Animals 

 as well as men are sensitive to barometric variations, as may be easily 

 verified by observation and experiment. It is not always essential to 

 carry animals up iu the air, or to take them down in diving bells that we 

 may observe the manner in which they are affected by an increase or 

 decrease of pressure, for the experimenter will also experience the 

 same effects, the nature of which is su(;h as to make the experiment 

 superfluous; investigation may be ('onducted in the laboratory where, 

 by means of special apparatus, it iS' possible to lessen the pres- 

 sure of air to any desired degree, or again to enhance it to ])oints 

 which startle imagination, to such points that the air is liqiu^fied, even 

 solidified. With proi)er apparatus we can at will obtain a virtually 

 absolute vacuum, or i)ressures of from 800 to 1,000 atmospheres; and 

 thus have no dilliculty in ascertaining the influence of atmospheric 

 pressure on animate life, and in coniirming the conclusions drawn from 

 the valuable researches made in this field by .lourdanet, Paul Bert, and 

 others. 



A circumstance that should be noted from the very outset is that all 

 beings, whether on land or in water, can stand without evil conse- 

 quences certain variations in atmospheric pressure. Man, for instance, 

 may work underground at a depth of 1 kilometer without suftering 

 inconvenience from the increased pressure, and may rise to altitudes of 

 5 or G kilometers in the air without fatal results from decreased pres- 

 sure. The same is true for birds and most mammals, and on the other 

 hand fish that live in great depths can rise to a ceitain level without en- 

 dangering life by lessened pressure, without bursting as they do when 

 they rise too near the surface. But it is none the less certain that in 

 vaiiations of pressure there are limits beyond which no living beings can 

 safely go, and that outside of such limits, which vary somewhat accord- 

 ing to species or groups, all beings die when the i^ressure is increased or 

 decreased. What is the process of death in both cases? That is the 

 question that confronts us. Let us first consider the case of decreased 

 pressure: what are the symptoms exhibited t Four hundred years ago 

 the Jesuit missionary, Acosta, gave us an excellent account of the 

 effects attending the ascent of high mountains, and conse(piently the 

 effect of rarefaction of air and decreased pressure. " While climbing a 

 mountain in Peru," says he, '• I was suddenly seized and surprised by 

 a distemper so deathly and so strange that I well nigh dropped from 

 my saddle to the giound. - - - Happening then to be alone with 

 an Indian, whom I begged to assist me in keeping astride of my horse, 

 I was taken with such a paroxysm of sobbing and vomiting that I 

 thought I wouhl surely die. - - - It only lasted for three or four 

 hours until we reached a nuich lower region. - - - And these 

 injurious effects are felt not only by men, but also by beasts."' - - - 



