126 



A DISCOURSE 



BOOK II. Thh'dhj, Fern is best destroyed by striking off the tops, as Tarquin did 

 "V"^^ the heads of the poppies : this done with a good wand or cudgel, at the 

 decrease in the spring, and now and then in summer, kills it, as also it 

 does nettles in a year or two, (but most infallibly by being eaten down, 

 at its spring, by Scotch sheep,) beyond the vulgar way of mowing or 

 burning, which rather increases than diminishes it. 



" ounces of the thirty-one ounces, to be carried off by respiration from the langs in the 

 " twenty-four hours ; (which I have found by certain experiment to be so much, if not 

 "more;) the twenty-five ounces multiplied by 438, the number of grains in an ounce 

 " avoirdupois, the product is 10,950 grains ; which divided by 254, the number of grains 

 " in a cubic inch of water, gives 43 cubic inches perspired by a man : which divided 

 " by the surface of his body, viz. 21 60 square inches, the quotient is nearly -^-^ part of a 

 " cubic inch perspired off a square inch in twenty-four hours. Therefore in equal 

 "surfaces, and equal times, the man perspires ^^jj, the plant or as 50 ; 15. Which 



" excess in the man is occasioned by the very different degrees of heat in each ; for the 

 " heat of the plant cannot be greater than the heat of the circumambient air, which heat 

 "in summer is from 25 to 35 degrees above the freezing point; but the heat of the 

 " warmest external parts of a man's body is 54 such degrees, and the heat of the blood 

 " 94 degrees ; which is nearly equal to water heated to such a degree as a man can well 

 " bear to hold his hand in, stirring it about ; which heat is sufficient to make a plentiful 

 " evaporation. 



" Qiu. Since, then, the perspirations of equal ai*eas in a man and a sun-flower are to 

 " each other as l65 * 50 ; or as 3J .* 1 ; and since the degrees of heat are as 2 ; 1, must 

 "not the sum or quantity of the areas of the pores lying in equal surfaces, in the 

 " man and sun-flower, be as Ij I 1.'' for it seems that the quantities of the evaporated 

 " fluid will be as the degrees of heat, and the sum of the areas of the pores taken 

 " together. 



" Dr. Keill, by estimating the quantities of the several evacuations of his body, found 

 " that he eat and drank, every twenty-four hours, 4 pounds 10 ounces. The sun-flower 

 " imbibed and perspired in the same time 22 ounces; so the man's food, to that of the 

 " plant, is as 74 ounces to 22 ounces, or as 7 * 2. But, compared bulk for bulk, the plant 

 "imbibes 17 times more fresh food than the man: for deducting 5 ounces, which 

 " Dr. Keill allows for ^hefceces aim, there will remain 4 pounds 5 ounces of fresh liquor, 

 " which enters a man's veins ; and an equal quantity passes off every twenty-four hours. 

 " Then it will be found that 17 times more new fluid enters the sap-vessels of the plant, 

 " and passes off in twenty-four hours, than there enters the veins of a man, and passes off 

 "in the same time. And since, compared bulk for bulk, the plant perspires 17 times 

 " more than the man, it was therefore very necessary, by giving it an extensive surface, 

 " to make a large provision for a plentiful perspiration in the plant, which has no other 

 " way of discharging superfluities ; whereas there is provision made in man, to carry off 

 " above half of what he takes in, by other evacuations. For since neither the surface of 

 " his body was extensive enough to cause sufficient exhalation, nor the additional reek. 



