Sept. 30, 1875] 



NATURE 



473 



up, which forced up the atmosphere to a prodigious 

 height, where it was chilled and its vapour condensed, 

 which fell in diluvial torrents, leaving the air so free from 

 vapour that radiation took place at an enormous rate, 

 chilling the earth and causing the glacial epoch ! He also 

 concludes that on account of the too great density of air in 

 the plain, man must have made his first appearance on ele- 

 vated plateaux, and he accounts in this way for the vene- 

 ration of high places among the early races. These and 

 similar speculations, though they may sometimes amuse, 

 do not detract from the real merit of the work in more 

 determinable matters. 



We reach the substantial part when we come to the 

 experiments of M. Bert, of which the results are here 

 given. Small animals were placed in chambers of various 

 capacities, which were then filled by the same absolute 

 quantity of air, necessarily at various pressures ; when 

 the animals were dead, the remaining air was analysed, 

 and it was found that in the larger vessels the proportion 

 of oxygen was greater, and this proportion was such that 

 the total amount of oxygen left was proportional to the 

 capacity of the chamber. The animals died as soon as 

 the oxygen by itself was reduced to a density of 4 per 

 cent, of what it would-be if the whole chamber were filled 

 with it at the normal pressure— the amount being thus 

 independent of the quantities of the other gases present. 

 This being true for any sized chamber, it follows we may 

 suppose the chamber indefinitely large ; and an animal 

 would die in the open air if the oxygen should have less 

 pressure by itself than 4 per cent, of 76 millimetres. 

 Taking the air to have its ordinary 21 per cent, of oxygen, 

 these experiments would appear to prove that life is im- 

 possible in air of less pressure than I4'5 mm. The pro- 

 portion of oxygen, however, seems to be much less than 

 that which is ordinarily supposed to be small enough to 

 produce asphyxia. Further experiments were performed, 

 pointing to the same result. Dogs were so fastened that 

 they could breathe only from a bag of limited size, and 

 from time to time the air in the bag and the blood of the 

 dog were analysed, and it was found that the oxygen in 

 both decreased sitnultaneously, though not at the same 

 rate. These and similar experiments, together with the 

 fact ascertained by M. Jourdanet, that the blood of 

 Mexican dogs contains a less proportion than usual of 

 oxygen, are the proofs offered that the blood cannot be 

 sufficiently oxygenised for health without a certain amount 

 of atmospheric pressure. 



In all these experiments, however, no allowance is made 

 for the possibility of the human lungs accommodating 

 themselves in time to the smaller pressure, so as to 

 enable the blood to take up a sufiiciency of oxygen ; and 

 this objection is seen by M. Jourdanet, who, after 

 giving an interesting account of the various evils that 

 have befallen noted climbers, discusses the question 

 whether an increased nirmber of respirations, or an 

 enlargement of the thorax, could counteract the effect 

 of the rarity of the air. As to the first, numerous 

 experiments on himself during his residence in Mexico 

 have enabled him to verify the law given by Leh- 

 mann, that the carbonic acid expired is in part con- 

 stant and in part only variable with the number and mag- 

 nitude of the respirations ; and he calculates from hence 

 that, in order to counteract the loss of pressure and dimi- 



nution of oxygen by increased respiration, it would require 

 twenty-four ordinary respirations per minute, which of 

 course the Mexicans do not make. As to the size of the 

 thorax, which has been stated by Forbes to be larger in 

 the inhabitants of these high regions, he objects that this 

 statement was made on too restricted data, and that 

 Coindet has found that it does not generally hold true. 

 Whatever may be the truth on this point, the explanation 

 which M. Jourdanet offers of the result of the low pres- 

 sure on the temperature of the body cannot be considered 

 satisfactory. He considers that, as a general rule, the 

 temperature of Mexicans is not below the average, 

 although their surface temperature often is,'and that the 

 loss of heat which would arise from the more easy radia- 

 tion and the lower oxygenisation of their blood is pre- 

 vented by "the repose of their functions," while their 

 respiratory organs are specially modified so as to be 

 capable of " exceptional exercise." The latter would 

 require proof, and as to the former, although the body 

 must lose temperature by the exact amount of work done 

 on external objects, " a care to avoid every effort " would 

 prevent the body doing work upon iiself, and less heat 

 would therefore be produced. The "apathy" of the 

 Mexicans and other inhabitants of high levels must have 

 another cause than this. 



M. Jourdanet's work ranges over a wide field, dis- 

 cussing, without much plan, various points in connection 

 with the climate of plateaux. Thus, in one chapter he 

 attempts to prove, by statistics of population, that the low 

 pestilential area round the Gulf of Mexico is more healthy 

 than the elevated table-land, the former having increased 

 six per thousand and the latter three per thousand in 

 forty-seven years ; that the decadence of the Peruvian 

 race is due to the influence of the atmosphere, without 

 apparently seeing the obvious objection that they must 

 have risen under the same influence, since they are a very 

 ancient race ; that the mental and physical work of the 

 Mexicans is below that of the inhabitants of the plains ; 

 and then he discusses the extreme height at which it is 

 possible to live permanently, which he places between 

 4,000 and 5,000 metres. This variety makes the book 

 very readable, but, in spite of its large size, the argu- 

 ments on many points are too brief to be convincing. 



The second volume is engaged in discussing the influence 

 of atmospheric pressure on disease, M. Jourdanet being 

 " convinced that the true nature of exterior influences is 

 far better seen in the maladies caused by them than in 

 the health which they favour." This portion of the work 

 has a principally medical interest, although some of the 

 results of his experience may be usefully mentioned. He 

 finds that consumption is rare in Mexico, and is princi- 

 pally confined to the poorer classes who have insufficient 

 nourishment, which he explains by their feebly oxygenised 

 blood being unfavourable to the development of the dis- 

 ease ; — typhus fever, on the contrary, finds there its most 

 suitable subjects, as do other inflammatory disorders, 

 while yellow and intermittent fevers are almost unknown. 



The elevation of the country where these observations 

 were made, and concerning which M. Jourdanet's con- 

 clusions have been arrived at, is 2,000 metres and over ; 

 and the climate of these places he speaks of as " climats 

 d'altitude ;" while intermediate heights he characterises 

 as " climats de montagne ;" to which latter he also devotes 



