Fires, most of which are of artificial origin, annually destroy much of our 

 forests. In the unprotected areas the damage, measured in acres burned, is 

 proportionately sixteen times as great as in the protected areas. Well-organized 

 fire patrols in the national forests have succeeded in preventing many fires 

 and in keeping the total fire damage down to a small fraction of what it is in 

 the privately owned forests. The chief damage done by forest fires is to young 

 growths; this prevents restocking. The rules for fire prevention in forests are 

 posted on trees, and every person who has occasion to go into the woods should 

 heed these regulations. 



Important but less serious dangers to forests are various species of insects 

 and various species of fungi. Every year these organisms destroy trees and 

 timber worth millions of dollars, and there is no one way to fight them all. 



Hand-to-Hand Fighting One way of dealing with pests is to go after 

 them directly when they show themselves. We slap every mosquito that 

 alights on our skins. We swat flies or pull a tomato worm from the vine. We 

 pull up weeds. Somehow weeds, flies and other pests seem to multiply faster 

 than we can pull them up or kill them. We look for wholesale methods. We 

 set traps to catch the enemy in large numbers: traps for rats and mice, for 

 Japanese beetles, for houseflies. These can work while we sleep or are other- 

 wise engaged. We place poison where we think it will do most good — for 

 mildews and for insects and other species. 



Barriers Where the enemy is known, we are often able to put up bar- 

 riers against his depredations. We may fence in our cattle against wolves or 

 quarantine them against infection, just as we screen our houses against flies 

 and mosquitoes. But keeping the enemy out is not always practicable, es- 

 pecially when we do not know the enemy well enough. For after all, how does 

 the liver-fluke get into the sheep? How do cattle "catch" Texas fever.? 

 How does the worm get into the apple? A large part of the research work of 

 the United States Department of Agriculture since the time of Lincoln has 

 had to do with learning the life histories of insects and other parasitic or 

 predatory animals and plants. These studies reveal to us not only the weakest 

 Jink in an organism's life cycle, but also the weakest links in the food chains 

 of which the species may be a part. 



According to such studies we find that when we cannot shut all the pos- 

 sible gates against an enemy, we can sometimes stop him in his tracks. By 

 destroying the barberry bushes in the regions that grow wheat, we make it 

 impossible for the wheat-rust fungus to complete its life cycle. In the case of 

 the liver-fluke, we find the key in ponds that harbor certain snails: no snails 

 in the pond, no liver-fluke in the sheep (see page 615). The alternate host of 

 the white-pine blister is the wild currant or the gooseberry. The most familiar 

 example of breaking the life-chain to control a pest is perhaps the case of the 

 mosquito. By draining swamps, covering rain-barrels, oiling ditches, we 



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