158 PRINCIPLES AND PRACTICE OF PRUNING 



of healing, and there is little evidence that it favors it, the slight 

 variation being no more than would naturally occur between two 

 sets of wounds treated in the same way. Those treated with pine 

 tar seem not to have healed quite so well as those untreated, al- 

 though the difference was not great. Coal tar, however, seems to 

 have been a positive hindrance to the healing process, not one 

 wound having been reported as healing extremely well, while the 

 majority [healed] only fairly well/* 



FIG. 117 STUDENTS' COMBINATION SAWS 



The upper tool shows the saw complete. The lower blades with the handle make 



up the set. 



132. Wound dressings.* Experience has recently shown the prac- 

 tical value of gas tar and forms of liquid asphaltum as wound dress- 

 ings. The relatively low cost of the gas tar, 15 to 20 cents a gallon, 

 and certain of its qualities, render it adapted to use for wound dress-* 

 ings. This material is not without limitations. One of these is a 

 certain difficulty in securing a continuous covering of sensible thick- 

 ness with the gas tar. Apparently very good results are secured by 

 using it in the semi-fluid or rather thick state, and this applies as 

 well to forms of liquid asphaltum made with linseed oil, etc. 



While at times, especially in cooler weather, it is desirable to heat 

 the gas tar, imperfect covering is secured with the very fluid, hot 

 tar. After cooling in part, a more favorable condition is reached. 

 In general, it would seem that two applications give more desirable 

 results. The second of these may be made after an interval of a 



* A. D. Selby, Circular No. 150, Ohio Agricultural Experiment Station. 



