•^12 C08M0S. 



tibly, although but slightly, <iver the sea and in the interioi 

 of continents, according to local conditions or to the seasons of 

 the year. We may easily conceive that changes in the oxy- 

 gen held in solution in the sea, produced by microscopic an- 

 imal organisms, may be attended by alterations in the strata 

 of air in immediate contact with it.* The air which Martins 

 collected at Faulhorn at an elevation of 8767 feet, contained 

 as much oxygen as the air at Paris. t 



The admixture of carbonate of ammonia in the atmosphere 

 may probably be considered as older than the existence of or 

 ganic beings on the surface of the earth. The sources from 

 which carbonic acid$ may be yielded to the atmosphere are 

 most numerous. In the first place we would mention the res- 

 piration of animals, who receive the carbon which they inhale 

 Irom vegetable food, while vegetables receive it from the at- 

 mosphere ; in the next place, carbon is supplied from the in- 

 terior of the earth in the vicinity of exhausted volcanoes and 

 thermal springs, from the decomposition of a small quantity of 

 carbureted hydrogen gas in the atmosphere, and from the elec- 

 tric discharges of clouds, which are of such frequent occurrence 

 within the tropics. Besides these substances, which we have 

 considered as appertaining to the atmosphere at all heights 

 that are accessible to us, there are others accidentally mixed 

 with them, especially near the ground, which sometimes, in 

 the form of miasmatic and gaseous contagia, exercise a noxious 

 influence on animal organization. Their chemical nature has 

 not yet been ascertained by direct analysis ; but, from the con- 

 sideration of the processes of decay which are perpetually go- 

 ing on in the animal and vegetable substances with which the 

 surface of our planet is covered, and judging from analogies 

 deduced from the domain of pathology, we are led to infer the 

 existence of such noxious local admixtures. Ammoniacal and 

 other nitrogenous vapors, sulphureted hydrogen gas, and com- 

 pounds analogous^to the polybasic ternary and quaternary com- 

 binations of the vegetable kingdom, may produce miasmata. « 



* Lewy, in the Comptes Rendus de V Acad, des Sciences, t. xvii.. Part 

 ii., p. 235-248. 



t Dumas, in the Annales de Chimie, 3e S6rie, t. iii., 1841, p. 257. 



X In this enumeration, the exhalation of carbonic acid by plants dur- 

 ing the night, while they inhale oxygen, is not taken into account, be- 

 cause the increase of carbonic acid from this source is amply counter- 

 balanced by the respiratory process of plants during the day. See Bous- 

 singault's Econ. Rurale, t. i., p. 53-68, and lAeh\^^& Organische Chemie, 

 8. 16. 21. 



<V Gay-Lussac. in Annales de Chimie, t. liii., p. 120; Payen, M4m. snt 



