MISCELLANEOUS NOTES. 



IN ascending from the low-lands, which arc elevated but little above the level of the sea, into the 

 higher mountainous regions, the interval between two successive respirations decreases in proportion as the 

 air becomes more rarefied. This fact may be accounted for by assuming that the lungs always require 

 nearly the same quantity of air in weight, and this quantity increases in volume in the same ratio, as the 

 density of the air decreases, but we cannot draw a larger volume of air in a single breath on a high moun 

 tain than at the level of the sea. 



In Mexico, near the level of the sea, I found that I breathed from twenty-two to twenty-three times in 

 a minute (the barometer standing at 760 millimetres or 30 inches), while in the city of Mexico, with the 

 barometer at 588 millimetres or 22.5 inches, the number of respirations in a minute was increased from 

 twenty-seven to thirty; at the llancho Tlamacas the barometer at 484 millimetres, the number was from 

 thirty-three to thirty-six, and at the crater of the Popocatepetl with the barometer at 406 millimetres, the 

 respirations were from forty to forty-four. 



Another scries of observations of a similar character relative to the frequency of the pulse, gave the 

 following results : Near the level of the sea I counted from sixty-four to seventy- four; at a height of 7500 

 English feet above the sea from seventy-five to eighty-four; at 12,800 English feet elevation from eighty- 

 six to ninety-four, and at the crater of the Popocatepetl, 17,300 feet above the level of the sea, from ninety- 

 six to one hundred pulsations in a minute. 



The observations on the frequency of respiration and on the pulsations, were made only when I felt 

 perfectly well, and was not in the slightest degree excited; generally after several hours rest, and in the 

 crater of the Popocatepetl early in the morning, before rising, after I had been sleeping ten hours or 

 more. Persons who are accustomed to live in low countries, experience considerable inconvenience for 

 some time after their arrival on the high plateau, in consequence of this acceleration of respiration, which 

 is particularly felt at every exertion, for instance in walking up hill, or only up stairs, in raising heavy 

 weights, etc.; but after they have lived for several months at these elevations, their breathing and pulsa 

 tions again become slower. The natives of the high table-lands probably do not breathe any faster or 

 have more frequent beats of the pulse than the natives of the countries near the coast, owing perhaps to 

 an increased capacity of the lungs. 



Similar observations have also been made on different animals, particularly on horses and dogs, which 

 had been imported from the low countries, llacc horses and gray hounds for instance, brought over 

 from the United States and England, have not the same speed on the high plains of Mexico as in their 

 native country. This, however, docs not affect the flectness of their offspring, if born and raised on the 

 high lands. 



At an elevation of more than 11,000 feet, a person in a good state of health never perspires, not even 

 after great exertions; and in an artificially increased temperature, only a feverish heat is experienced. Even 

 at the height of the city of Mexico, anything more than a slight perspiration is rarely felt. It has been 

 before stated, that I never observed a case of bleeding of the nose, whilst ascending very high mountains, 

 but generally headache, accompanied by a painful sensation in the eyes, which swell out considerably, is 

 felt. The odor of sulphur, besides the rarefied air, is one of the principal causes of this pain, as it is 

 much more severe at the bottom of the crater of the Popocatepetl than near its edge or outside. 



During the rainy season, from June to September, the tops of the higher mountains are rarely seen, 

 as they arc almost constantly enveloped in clouds or fog, produced by the contact of the warm air (at 

 this season, nearly saturated with humidity) with the cold, partially snow-covered surface of the moun- 



