Public Parks. 41 



duced, and exposed to the action of the sun, the carbonic acid will 

 be absorbed, and the air restored to its original condition. The 

 putrefaction of animal matter, and the decomposition of vegetable 

 substances, would cause a sufficiency of carbonic acid vapor, when 

 united with atmospheric air, to destrov every living being, were 

 it not for this wise provision of nature. This gas, which is 

 poisonous to the human as well as animal species, is a source of 

 nutriment to every variety of plants ; and thus, it would appear, 

 exercises a benign influence in protecting man from the deleterious 

 effects of poisonous vapors. And if the effect is obtained, so far as 

 regards one species of poisonous vapor, it may be equally so in 

 reference to that giving rise to fever." * 



Dr. Cartwright ascribes to the yussicea gtandijlora., a plant 

 found in great abundance in marshy or swampy places in the 

 Southern States, particularly in certain regions of Louisiana, which 

 present the usual characteristic malarial surfaces, the cause of 

 their exemption from fever, f Aquatic plants and those found in 

 swampy or marshy soils while growing, exhale a large quantity of 

 oxygen ; but when they have their growth, this action ceases and 

 those regions become imhealthy. It was at one time supposed that 

 no ozone could be found in swamps ; but I have discovered its 

 presence in June, near the surface of the water of a lake in which 

 the Chara were growing abundantly, but could not detect it in the 

 same place in September. It has also been ascertained that fish are 

 healthier and thrive better in water where aquatic plants are found 

 than where they are absent. 



A distinguished natural philosopher, Changevix, inferred from 

 the results of his experiments, that the action of trees in producing 

 the effects under consideration, is two-fold. "Plants," he says, 

 "whether odoriferous or inodorous, give issue to emanations which, 

 when mixed with poisonous vapors exhaling from marshy or damp 

 soils, neutralize their pernicious influence. But the former exercise 

 a greater effect through means of the neutralizing process than by 

 the power of absorption just mentioned, their emanations mixing 

 with the air we breathe and correcting its deleterious properties by 

 virtue of the particular qualities with which they are endowed. 

 The second class — the inodoriferous — on the other hand, act more 

 evidently through means of their power of absorption than of the 



* Medical History of Alabama, 

 t Western Medical Journal. 



