94 Curatke Influence 0/ th6 



frequently experience a rupture of small vessels, which are distri- 

 buted on the membranes most exposed to these influences ; it is 

 therefore easy to conceive, that injurious consequences may result 

 from slight elevations, to invalids, the delicate vessels of whose 

 lungs have either suffered partial disorganization, or have acquired 

 an increased degree of susceptibility to disease. 



** This increased rapidity in the circulation, and in respiration, is, 

 nevertheless, by no means proportioned exclusively to the degree of 

 elevation to which the individual is exposed, but is not less affected 

 by constitutional peculiarities ; hence evidently the cause, why so 

 much discrepancy exists between the accounts given by authors, 

 of the sensations they have experienced at different altitudes. 



" Thus, although M. Saussure informs us, that on ascending 

 Mont Blanc, he suffered from these effects in a very high degree, 

 that his strength became exhausted, and that various febrile symp- 

 toms evinced themselves ; and although Sir W. Hamilton felt great 

 difficulty in his respiration on Mount Etna, and many have been 

 attacked by haemoptysis and other haemorrhages, under similar cir- 

 cumstances ; Dr. Heberden did not complain of any very material 

 inconvenience from visiting the Peak of Teneriffe, and the same 

 may be observed of several others, who have reached the heights 

 of Mont Blanc and parts of the Andes ; and even Of those who 

 have experienced the rapid ascent of balloons. 



" But, notwithstanding these facts, when we consider, that in 

 low situations, and with the barometer at thirty inches, we sustain 

 an atmospheric pressure of fifleen pounds upon every square-inch, 

 or thirty-two thousand pounds weight on the whole surface of the 

 body, elevations, great or small, as well as changes in the state of 

 the atmosphere, by each of which, this external pressure is often 

 suddenly diminished several thousand pounds, necessarily exert a 

 powerful influence on the delicate structure, and functions of the 

 lungs, when the health of these organs is in any way deranged. 



" From various experiments, which have been at different times 

 undertaken, with a view to determine the effects produced by a 

 light, and a heavy atmosphere on the function of respiration, we 

 learn, that, although animals become subject to such serious incon- 

 venience from the partial exhaustion of the air, within the receiver 

 of an air-pump ; on the contrary, by the condensing machine, they 

 sustain a degree of pressure equivalent to the weight of three or 

 four atmospheres, without apparent injury ; and that, after an ani- 

 mal has been subjected to this extreme pressure, it seems to expe- 

 rience the most uneasiness in returning to that of its accustomed 

 medium. 



*' In the first instance, there can be little doubt that the incon- 

 venience does not depend more on the primary abstraction of the 

 air, and the scanty supply of oxygen which so rare a medium can 

 afford, than on the suffocating effects produced by the distension of 

 the blood-vessels lining the minute air-cells of the lungs, by which 



