'Chap. 3 . ] Circulation of t'he Fktias . 21 



our lenfes, and which the contact of -a body of fire is 

 fometimes capable of inflaming, as has been obferved 

 with regard to the fraxinella. 



c Some botaniits, obierves Dr. Bell, f have con- 

 ceived, that plants, as well as animals, have a regular 

 circulation of therr fluids. Others think this very im- 

 probable. Or, both fides, recourfe has been had to' 

 experiments ; and from thefe, conclufions pierfeclly 

 oppofite have been deduced. When a ligature has 

 been fixed round a tree, in fuch a manner that no juice 

 could be tranfmitttd through the bark, the tree has 

 been found to thicken above the ligature ; but below 

 it, to continue of the fame circumference. Hence 

 fbme Jiave -concluded, that the fap afcends through the 

 wood, and defcends through the bark, Thofe who 

 are of a contrary opinion have found, that, in certain 

 cafes, the juice afcends through the bark only: for 

 v/hen a portion of the wood has been cutout, and the 

 bark exactly replaced, the growth of the tree has been 

 found to go on unchanged : hence it, is faid, that the 

 juice is tranfmitted equally through all parts of vege- 

 tables. The experiments adduced on each fide of the 

 queftion are juft, but the reafonings on thefe, by each 

 party, feem equally inconclufive. The analogy of ani- 

 mal nature appears to favour the opinion, that the juice 

 rifes through the wood only, and defcends only through 

 the bark ; but this analogy is not complete through- 

 out. The arteries are not placed in the internal parts 

 alone, nor the veins in the external, but they accom- 

 pany each other through every part of their diftribu- 

 tion. In, vegetables, th fap rifes from the roots, but 

 the proper juice defcends towards them -, in the defcent 

 of the juice, the wood acquires its growth, and ab- 

 ibrption is a conftant aftion of the leaves. Thefe cb- 

 lervations render it probable, that there is a circulation 



