NOTES ON HISTORY AND CLIMATE OF NEW MEXICO. 327 



any other season of the year, and therefore the air being dry, the greater 

 actual cold than in lower climates is felt less severely, and if the body 

 is warmly clad the lowness of the temperature exerts only its tonic influ- 

 ence. The air being rarefied, the sun has a much greater influence, be- 

 ing more constantly visible in mountainous districts, and enables the 

 enfeebled invalid to spend several hours almost daily in the sunshine 

 with very great advantage. (Page 32, "Manitou, Colorado, U. S. A.; 

 its mineral-waters and climate." Saint Louis, J. McKittrick & Co., 

 1875.) 



Dr. Solly refers to the fact that oxygen is essential to procure change 

 of substance, and as it diminishes in proportion to the elevation above 

 sea-level, it might be supposed that healthy change of substance would 

 be retarded in mountain air ; " but this," he adds, " is practically found 

 to be otherwise, and the reason doubtless is that, as only about 25 per 

 cent, of oxygen is on an average used in respiration, there is probably 

 more than sufficient oxygen at any height that has as yet been attained 

 by man." 



The discussion as to the gases of the blood, their ratio to other con- 

 stituents, condition of the oxygen as free, mechanically dissolved there- 

 in, or chemically combined, or both, I have no disposition to continue; 

 but in so far as atmospheric pressure may be considered an important 

 cause of variation, we have the statement of Lehman (Physiological 

 Chemistry, vol. 1, p. 572) that " Liebig is certainly in the right when 

 he advances the proposition that ' a gas can only be considered as me- 

 chanically absorbed when its quantity increases and diminishes in pro- 

 portion to the external pressure.'" We think we are justified in conclud- 

 ing with Liebig that the quantity of oxygen which may be absorbed by 

 the blood is constant in amount, and, to a certain extent, independent 

 of external pressure — an opinion which is based partly on the fact that 

 the respiratory process is carried on nearly the same, both at very great 

 heights and at the level of the sea ; and that no more oxygen is absorbed, 

 even in an air very rich in oxygen, than in the ordinary atmosphere." A 

 certain amount of mechanical difificulty, labored respiration, on ascend- 

 ing heights rapidly is generally experienced. At the same time, the 

 very great strain put upon the muscles of locomotion causes pain in the 

 limbs. We have no reason to expect the muscles of respiration to bear 

 undue exercise and strain without fatigue, and it very probably contrib- 

 utes largely to what is known as dyspnoea, which is experienced as 

 severely after rapid running any distance upon a plain. The question 

 might be asked to what extent a diminished atmospheric pressure might 

 facilitate the escape of carbonic acid from the lungs 1 May it not be far 

 more imi^ortant to free the blood rapidly of its carbonic acid, which is 

 poisonous, than to inhale and accumulate oxygen in excess of the need 

 of the system and the chemical capacity of the blood to utilize ? 



The extent to which diminished pressure alone may affect respiration 

 can best be determined by the aeronaut, who reaches a height without 



