TREATMENT OF OLD WOUNDS. 53 



defects of this nature : it can with proper application, 

 however, arrest the progress of the evil, and in such 

 cases should always be resorted to. The edge of the 

 cavity should be cut smooth and even ; and all de- 

 composed matter, or growth of new bark formed in 

 the interior, should be carefully removed. A coating 

 of coal-tar should be applied to the surface of the 

 cavity, and the mouth plugged with a piece of well- 

 seasoned oak, securely driven into place. The end 

 of the plug should then be carefully pared smooth 

 and covered with coal-tar, precisely as if the stump 

 of a branch was under treatment. If the cavity is 

 too large to be closed in this manner, a piece of thor- 

 oughly seasoned oak-board, carefully fitted to it, may be 

 securely nailed into the opening and then covered with 

 coal-tar. It is often advisable to guard against the 

 attacks of insects, by nailing a piece of zinc or other 

 metal over the board, in such a way that the growth 

 of the new wood will in time completely cover it. 



These operations resemble, if such a comparison 

 is admissible, the fillings performed by dentists, and 

 with the same object, to check the progress of 

 decay. 



A glance at Fig. 50 shows what takes place when 

 cavities in the trunks of trees are treated in the man- 

 ner recommended. On the right a cavity treated in 

 this manner is shown. New layers of healthy straight- 

 grained wood have already formed ; the circulation 

 of sap is regular and healthy ; and the tree is entirely 

 restored to health. On the left an old neglected 



