118 On the Malaria of the Campania di Roma. 



The effect has also been imputed to exhalations of azotic gas; 

 but this gas being lighter than atmospheric air, would necessarily 

 rise, and thus render the heights more unhealthy than the val- 

 leys, while experience proves that the contrary is the fact *. 



The Campagna of Rome is an extended country, cut up by 

 little hills, and mostly in an uncultivated state. During the 

 rainy season, the water collects in the valleys, and forms pools 

 where it stagnates ; and having brought with it all sorts of ve- 

 getable substances, as well as animal refuse, it becomes cor- 

 rupted. At the return of the warm season, which augments the 

 putrefaction, these ponds and marshes send forth their vapour; 

 but as the process of evaporation goes on slowly, the heat being 

 still moderate, the atmosphere is not much changed, until the 

 month of July brings with it a greatly increased temperature, 

 which accelerates the evaporation, and which is accompanied by 

 fevers whose duration equals its own, that is to say, it is pro- 

 longed to September. 



If the Campagna were every where properly cultivated, as it 

 was formerly, the air would not be subject to the alteration ; 

 for the rains of winter would not then collect as they do in the 

 low grounds, but would be absorbed by a mellowed soil, and 

 evaporated by the influence of the heat. 



It must not be urged against this opinion, that in Lombardy, 

 especially in the plains which extend from Bologna to Ferrara, 

 the vast fields of rice are, during the whole winter, covered with 

 water, and that the country is nevertheless not unhealthy, or at 

 least not so much so as that of Rome. These artificial lakes or 

 inundations, as I have myself observed, are first, on account of 

 their extent, always agitated by the wind, like a lake of water, 

 . and also by the action of the sluices, by which they are supplied 

 and drained ; the current of water is continually entering and 



• While we admit with the author, that azotic gas is not the probable 

 cause of epidemic fever, we must object to the soundness of his conclusion 

 with respect to its elevation. Although somewhat lighter than atmospheric 

 air, it is, we believe, most conformable to established facts in chemistry, to 

 conclude, that the particles of any gas, if set free in the atmosphere, will 

 [ultimately] arrange themselves in the same manner as if the atmosphere 

 itself did not exist, provided they have no affinity for, or do not combine 

 with, the constituents of the air. 



