Theories and Experiments 273 



M. Liguistin himself realized that this element might have an 

 important etiological part: 



Certainly there is no doubt (he says himself) that at the season 

 when we crossed Rio-Frio, the period of great heat, that a consider- 

 able increase in the temperature, causing evident rarefaction of the 

 air, added to an elevation of 3302 meters above sea level, and 

 producing by this altitude a decrease of 3 ¥2 kilometers in the height 

 of the atmospheric column, had the immediate result of decreasing 

 considerably the quantity of respirable air and producing symptoms 

 characteristic of such causes. We should have liked to be able to 

 prove this physical point by the barometer, during the different 

 conditions of the atmosphere; for that alone would have furnished 

 the real explanation of the swelling of the abdomen frequently 

 appearing in the animals of the expeditionary corps during our 

 crossing of Rio-Frio. However, although this rarefaction was not 

 demonstrated experimentally, its existence is nevertheless undeniable. 



In Mexico City, observation showed that the atmospheric pressure 

 was only 58 degrees. We may therefore estimate it for Rio-Frio at 

 approximately 55 or 56, which would cause a decrease of 20 degrees 

 from normal atmospheric pressure. Is it illogical to suppose, after 

 that, that animals cannot be placed for even an instant in such a 

 medium without their organism feeling some effects of it? Evidently 

 not; and we were all the distressed, but not surprised, witnesses of 

 the harmful effect which so rarefied an atmosphere can produce upon 

 the health of large solipeds; I mean this second pathological scene, 

 which appeared again more definitely at Rio-Frio, and which brought 

 a moment of turmoil and confusion (indigestion with distention). 

 (Vol. IV, p. 262.) 



In short, M. Liguistin persists in the idea of poisoning, the 

 harmlessness of which he explains by the partial neutralization 

 produced by other plants simultaneously ingested. By searching 

 in the vicinity, they found a sort of scilla, to which they attributed 

 the symptoms. Experiments made with the leaves suspected gave, 

 however, only one interesting result: the firm refusal of the horses 

 to taste them, even after a fast of 48 hours. As for poisoning 

 obtained by aqueous extract, ingested in the animals by force, 

 they by no means resemble the symptoms observed during the 

 crossing of Rio-Frio. Whence we conclude, in direct opposition 

 to our author, that these symptoms were due exclusively to the 

 rarefied air. 



I now come to the article of M. Leroy de Mericourt, 111 an article 

 to which the name and the special qualifications of its author 

 gave much credit, and which is still quoted constantly. 



However, it does not contain any personal observation, and the 

 only really original idea in it is due to Professor Gavarret; but 

 it gives, in an elegant style, a summary of the data previously 



