\ ■ 



As to the other two questions, I have made great use of data 

 given by authors who have discussed these topics, and I think that 

 my own studies will not be without value in guiding physicians 

 and hygienists in the midst of the innumerable difficulties which 

 these questions involve. But I have not handled them directly, not 

 only because of my medical incompetence, not only because labora- 

 tory experiments on birds, dogs, or even men could hardly settle 

 them, but also for a special and rather personal reason. 



Eight years ago, when Dr. Jourdanet, well known for his re- 

 markable studies on the climatology of Mexico and for his theory 

 of the anoxemia of altitudes, offered— with a generosity for which 

 I hope the results of my work might be worthy recompense— to 

 put at my disposal all the material means required by the re- 

 searches whose importance and difficulty I had publicly indicated x 

 in 1868, a sort of tacit agreement was established between us. I 

 was to limit myself to studying experimentally in the laboratory by 

 means of my instruments the modifications which changes in baro- 

 metric pressure would produce in the vital manifestations of ani- 

 mals or plants. Whatever the extent of my experimental equip- 

 ment, these changes evidently could not be of long duration, so 

 that if they were to produce convincing results, it was absolutely 

 necessary that they should be extensive. Besides, this is the pe- 

 culiar characteristic of laboratory experiments. 



M. Jourdanet properly reserved for himself the study of the 

 effects produced by slight variations in barometric pressure, acting 

 either for a rather brief time upon invalids — a test the exquisite 

 delicacy of which will always terrify experimenters a little— or for 

 years upon the same individuals, or for centuries upon successive 

 generations, joining their effect to those of so many causes known 

 or unknown; dangerous problems, but very likely to fascinate a 

 wise and eager spirit, aided by an eloquent pen. 



We both accomplished our tasks; two years ago, M. Jourdanet 

 published his fine book, Influence of Air Pressure on the Life of 

 Man: Altitude Climates and Mountain Climates. 2 



As for me, delayed by efforts outside the field of science, too 

 often called from my laboratory by important civic duties, it is 

 not until today that I present the properly arranged results of my 

 long researches. 



The present book which, if I am not mistaken, holds interest not 

 only for physiologists, but also for physicians, engineers, and even 

 travelers, is divided into three parts: history, experiments, con- 

 clusions. 



XVII 



