238 M. Paul Savi's Co7mclcrnt.io7is on the 



circumstances which are peculiar to it, viz. the exclusive vege- 

 tation of the Chara, and the supply of the lake with thermal 

 waters. The author performed some experiments which 

 prove, that in a limited atmosphere, the emanations Irom the 

 Chara, when decomposing, acted mischievously on the eco- 

 nomy*. They might therefore in part produce the delete- 

 rious action of the waters of this lake. But as the Chara does 

 not exist in many other unhealthy marshes, and does vegetate 

 in healthy situations, the cause of the insalubrity of the air 

 cannot be attributed to it in all cases. 



An examination made by M. Savi showed that much gas 

 emanated from the bottom of it ; it contained carburetted and 

 sulphuretted hydrogen, and these were in the largest pro- 

 portion. The author, on well-known chemical grounds, attri- 

 butes the existence of sulpliuretted hydrogen to the reduction 

 of the sulphates into sulphurets b}' the influence of decom- 

 posing organic matter: analysis showed that the proportion 

 of sulphurets is smaller in the lake than in the mineral waters 

 which flow into it. The author does not venture yet to 

 decide on the question whether the insalubrity of the air is 

 derived from the sulphuretted or carburetted hydrogen, or 

 to putrid miasmata, the production of which would be pro- 

 portional to that of these two gases; he is satisfied with re- 

 marking the prominent circumstances occurring in this local- 

 ity — the presence of mineral waters in a soil containing de- 

 composing vegetable matters, and the presence of sulphates in 

 these waters. 



Insalubrity caused by Putrefying Alg(E. 



The author states that this putrefaction occurs in those 

 places in which collections of algae are washed by fresh water 

 mixed with sea water ; the decomposing vegetables exhale 

 a perceptible smell of putrid eggs, and these places become 

 centres of insalubrity : intermittent and more dangerous fevers 

 prevail there. He cites as an example the port of Vada, 

 Porto Nuovo of Piombino, the ancient port of Taiamone, 

 &c. The presence of sulphuretted hydrogen gas has been 

 demonstrated in the products of the putrefaction : some ex- 

 periments have proved that the aigaj do not putrefy in pure 

 water so as to disengage sulphuretted hydrogen ; the presence 

 of sulphates being necessary. This putrefaction, at any rate, 

 is not peculiar to the algsa alone, but to many vegetables car- 

 ried into sea water. 



* Rcchcrchvs Physiques ct Chimujucs sur Ic Chara ou Patera , 1 83^. 



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