61 



the canker the exciting, but only the pre- 

 disposing cause of the vermin; as is the 

 rending of the bark, wounds, injuries, &c. 

 and I do not find that these produce even 

 topical canker, in a tree not bark-bound. 

 So woffnds on the animal body in good 

 habit, heal up without any bad consequence ; 

 whilst, on a bad habit, the slightest scratch 

 often becomes serious, and sometimes fatal. 



The stricture of the bark, however, must 

 be viewed in a very different light ; for it is 

 undoubtedly the general cause of the 

 canker, by not allowing the juices to dis- 

 perse freely over the tree, which bursting 

 out at any weak part, form with the bark, 

 this ragged substance called canker. For 

 we know, that all stagnant animal and ve- 

 getable juices, when exposed to the air, are 

 much given to putrefaction, and communi- 



