CONTROL OF DISEASE. 59 



est amount of high-grade merchantable timber, acts as 

 a. parasite on the whole community ; it takes space, light, 

 and food from the sound trees and places them in con- 

 stant danger from infection, attack by insects, and fire. 

 The forest is a community of living trees, which 

 breathe, assimilate food, grow, adapt themselves to sur- 

 rounding conditions, and struggle for life, and which 

 are subject to diseases and injuries from which they 

 may succumb if not helped in time, exactly like any 

 other plant and every animal. The forester in charge 

 of these living beings must endeavor to eliminate any 

 danger to their health, to prevent their injury, and to 

 establish sound conditions for their growth. These are 

 the objects of forest hygiene, upon the application of 

 which the welfare of the community depends. 



The first step in any hygienic work is close observa- 

 tion. Unless the field man keeps a sharp lookout for 

 signs of disease or abnormality in individual trees, he 

 will in all likelihood fail to see an unhealthy condition 

 in the stand and so lose the opportunity to remedy it. 

 Under " Symptoms of disease," page 18, a number of 

 hints are given on how to recognize any trouble. 



There are a number of injurious factors which we 

 can not control, such as lightning, drought, and floods. 

 Fires which can be controlled have more to do with 

 decay of forest trees than is commonly supposed, since 

 fire scars very often offer an easy entrance to wood- 

 destroying fungi and to wood borers. 



It is manifest that expensive measures, such as treat- 

 ment of wounds, pruning, spraying, and the construc- 

 tion of isolation ditches, can not be applied in our enor- 



