GENERAL METHODS 131 



less heavy than asphalt, unless it is a perfectly 

 drained basal cavity, in which case coal tar can be 

 used. Whatever material is chosen, it must be 

 applied after the braces are in, and the applica- 

 tion must be thorough and absolutely complete. 



FUMIGATING 



If boring insects have gained entrance through 

 the trunk, and have progressed beyond the decay, 

 so that some remain after the decay is removed, 

 the cavity must be fumigated before it is filled. 

 Tack a sheet of tar-paper over the mouth of the 

 cavity, filling the interstices between the paper and 

 the bark with clay or cotton-batting dipped in mud. 

 Just before the last corner is packed down throw 

 in a rag soaked with a teaspoonful of carbon bi- 

 sulphide for each cubic foot of space in the cavity. 

 If the cover is tight the larvae will be dead in a 

 few hours. 



FILLING: CHOICE OF MATERIAL 



The cavity is now ready for filling. The first 

 question in that connection is the choice of a filling 

 material. Concrete is still generally looked upon 

 as probably the best filler for the more simple 

 types of cavities, although its shortcomings and 

 limitations are constantly being more widely recog- 

 nized. Its advantages are that it is very cheap, is 

 easily obtainable everywhere, requires none but 



