TREATMENT OF WOUNDS 33 



transverse cut and is then to a certai^i extent sub- 

 ject to the drawbacks attendant on the use of such 

 materials as creosote. It does not adhere well to 

 moist surfaces, blistering up easily. On large 

 wounds it must be frequently renewed. For in- 

 stance, the writer once had to treat a large bark 

 wound in an ironwood tree. The exposed wood 

 was dry and sound, though rather deeply cracked. 

 He applied at intervals of a week or two, during 

 the summer, four thorough coats of tar. The 

 conditions were ideal for a perfect job. Four 

 years later there were numerous holes through the 

 tar where insects had escaped and there were even 

 cracks through which the wood was visible. This 

 does not prove that tar is not a valuable dressing. 

 It only shows that in this case four years was too 

 long to wait before renewing the protective cover- 

 ing. That is the great point about the use of tar. 

 It must be renewed at frequent intervals. How 

 long those intervals can be depends upon circum- 

 stances. If a thorough second coat is given 

 rapidly-healing pruning wounds up to say six 

 inches in diameter, a year after the first coat, they 

 can usually be left to heal without further atten- 

 tion. Larger wounds should receive a second 

 coat the year after the first one and every second 

 year thereafter, until checking absolutely ceases 

 and a heavy impervious layer of tar is formed 

 over the whole surface. 



