TEEMITES IN THE UNITED STATES. 27 



to crack, allowing avenues of ingress, and the beams and joists 

 put down in the moist material soon partially decay and become 

 exceptionally good breeding places. From such beams the white 

 ants carry their burrows up through the timbers of the first and 

 even second floors (Marlatt). Flooring commonly becomes infested 

 through the wooden beams or stringers laid directly on the earth 

 or in moist concrete; untreated beams should never be laid on the 

 earth and the spaces filled in with concrete, or in moist concrete, 

 since they will rot, even if they do not become infested. An air space 

 should intervene. Therefore the foundations of buildings should 

 be entirely of brick, stone, or concrete, including the basement 

 floor, without beams or joists sunken in the ground or concrete, 

 and especially should this method of construction be followed in 

 tropical and subtropical regions. H. von Schrenk, of St. Louis, 

 Mo., states that in no case should timber joists be completely sur- 

 rounded with mortar or brick; there should be an air space com- 

 pletely around the joists so as to permit air circulation. 



Marlatt states that complete dryness is an important means of ren- 

 dering buildings safe from attack. Books and valuable documents, 

 etc., should not be packed away in unventilated chambers where they 

 may become moist and moldy, as they are then particularly subject to 

 attack by white ants, which are very likely to be present in old build- 

 ings, even though their work has not been sufficient to bring them into 

 special notice. 



USE OF RESISTANT WOODS. 



Certain species of woods are highly resistant to termite attack, due 

 to the presence of oils, alkaloids, gums, or resins as well as to hardness 

 and other factors. 



Maj. George Ahern, United States Army, reports, according to 

 Marlatt, that California redwood has been used for more than 25 

 years in the Philippines and has never been known to be injured by 

 white ants. Its use in Manila is very general, especially in the con- 

 struction of cabinets, filing cases, etc., where it is desirable to protect 

 valuable papers from these insects. Eedwood is not resistant against 

 termite attack in contact with the ground in California. 



Another resistant North American cabinet wood is black walnut; 

 of the tropical species, teak, mahogany, and " peroba " are resistant 

 woods. 



As to timber to be set in contact with the ground, E. Gerry gives 

 data 1 on the durability of native hardwoods ; of the conifers, incense 

 cedar, eastern red cedar or juniper, western red cedar, and southern 

 bald cypress are resistant. Durable and resistant exotic structural 



1 Gerry, Eloise. Tyloses : Their occurrence and practical significance in some American 

 woods. In Jour. Agr. Res., v. 1, no. 6, p. 445-470 (p. 463-464), pi. 52-59, Mar. 25, 1914. 



