166 On Malaria. 



strangers and respectable inhabitants quit Rome, and thus the 

 gigantic city is half depopulated. 



From all my observations, which at present I have not time 

 to develope, I believe I may deduce the following conclusions : 

 First of all, it is necessary to distinguish malaria from marsh 

 fevers ; and this we may do, either by considering the form or 

 the cause of the disease. To throw every thing together with- 

 out further proof, is to give rise to uncertainty, and to form a 

 chaos in the present state of our knowledge. When we take 

 into consideration all the phenomena of marshy districts, the 

 conclusion does not lie far distant, that the atmosphere is in dif- 

 ferent degrees rendered unfit for human organisation, not by 

 the passage of the water to the air, but by the decomposition 

 and solution of vegetable substances ; that thus those various 

 intermitting fevers, and even the plague itself, are produced by 

 the Adriatic Sea ; that the removal of those diseases, though 

 they certainly are most frequent in summer, is not connected 

 with any particular period ; and that, consequently, though 

 marshy regions are avoided, yet in these emigration does not in- 

 variably take place. In the case of real malaria, in opposition 

 to marsh fevers, the circumstances are different. So long as 

 the earth is covered with Uving vegetables, as for example with 

 corp, the air of the most suspected district is pure and healthy, 

 and no one fears being attacked by the disease ; but when 

 the prodigious crops, which in those volcanic, loose-soiled 

 districts are speedily brought to maturity, are removed, does 

 the surface of the earth become dead at the warmest and most 

 energetic period of its functions .? or does not rather a portion 

 of those substances, which were consumed by the leaves and 

 roots of plants, now go to the atmosphere and render it un- 

 favourable for the breathing of man, until all is again restored 

 to an equilibrium in higher or more distant regions. That car- 

 bonaceous matter is beneficial to the vegetable kingdom, is as 

 well known as that it is prejudicial to the breathing process in 

 animals. That in Rome the higher parts of the town, as the 

 Trinita del Monte, the Capitol, &c. are free from malaria, while 

 low-lying districts, as the campo vaccino, &c. are very danger-, 

 ous, is certain, and confirms the view we have given. On the 

 appearance of malaria the Pope leaves the low lying Vatican, 



