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Dr. Holyoke's Edlmi^tc of the Excess of Ileal ai}^ Cold. 73 



All vegetables tlien^ both in Europe and America, are 

 continually supplying the atmosphere with this pure air^ 

 iind counteracting those pjilogisticating processes, such as 

 combustion, respiration, putrefaction, &c. "whicli are con- 

 tinually going on in all parts. But there is this material 



diJBference between the two continents. In Europe, upon 

 the coming on of the frosty season, the leaves of all vegeta- 

 bles, on or near the earth's surface, languish; and, if they 

 do not die, yet most probably they perform their office of 

 dephlogisticating the air, in a much more languid manner, 

 than in summer; or are perhaps entirely covered with snow, 

 w^hich, while it continues on them, must effectually put a 

 stop to this process ; and a?^ to the trees, their leaves for the 

 most j)firt drop off, and no more pure air is to be expected 

 from them, till they are again renewed in the spring. But 

 in America, although the leaves of all vegetables on the 

 earth's surface are frozen and killed early in the winter, and 

 the leaves of many of our trees fall off, and yield no more 

 of this pure air, than the European trees; yet, there is a 

 constant and large supply of it, from those vast quantities of 

 pine trees, firs, spruce, cedars, junipers, savins, hemlocks, 

 and other ever-greens, which retain their leaves through the 

 intensest frosts, and which do greatly abound in our Ameri- 

 can woods, from the 30th to the 50th degree of N. latitude ; 

 a quantity sufficient, perhaps, to cover one 5th or Gth of the 

 whole surface of the continent of Europe. 



That our evergreens do in fact yield, during the winter 

 season, such a pure air, I have several times found by expe- 

 riment. My experiments were conducted in the manner. 



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