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probable that a good many mosquitoes are destroyed among the 

 other insects, especially when larger insects are scarce. 



Mr. Bishopp's description of the Campbell bat roost is as 

 follows : 



The Campbell bat roost consists of a sort of tower set on four 

 posts about ten feet above the ground. According to Doctor 

 Campbell, the size of the roost may be varied considerably. As 

 I recall them, the dimensions of the roost at Mitchell Lake are 

 about as follows : Twelve feet square at the bottom, the walls 

 slanting inward toward the top which is about six feet square. 

 Height, about twenty feet. On the outside the building is 

 covered with drop siding with tar paper beneath. The roof is 

 shingled and projects over the edges. It is slightly elevated so 

 as to permit of the entrance and exit of the bats. Additional 

 entry space is allowed entirely down one side of the building. 

 This opening, which is about two and one-half feet wide, is 

 provided with boards slanting upward so as to exclude light to 

 some extent but allows the bats to enter between them. The 

 central portion of the house from, the side provided with the 

 entrance to the opposite side is unobstructed from top to bottom 

 thus leaving an air space about two and one-half feet wide. On 

 each side of the shaft, and running to the two other sides of the 

 building*, is a series of shelves made of matched flooring. These 

 shelves slant upward and outward at about an angle of thirty 

 degrees. In the first house constructed these shelves were about 

 five inches apart, but I believe in the later model they are closer 

 together. Wire netting is tacked on top of each of the shelves 

 so as to provide places for the bats to hang. The slant is given 

 so as to allow the guano to roll down and drop into the center of 

 the bottom structure which is provided with trap doors opening 

 downward. This is to permit of the emptying of the manure 

 into a wagon which is placed under the roost. 



The following interesting letter bearing on this subject was 

 received in 1912 from Dr. Byrd, the well-known health officer of 

 Florida : 



