TEE AIR OF THE LUBAY GAVERN8. 559 



we can not without repugnance step into the illuminated area and 

 breathe. Such an experiment in a room in Limair reveals scarcely 

 a particle of dust floating in the air; *. e., the air is optically pure. 

 Noting this fact, I became interested in the bacteriologic condition, and 

 determined to visit Luray again, supplied with culture media and 

 sterile plates. 



In December, 1902, fitted out with five dozen sterile plates and six 

 dozen tubes of agar-agar, I spent four days at Luray studying the 

 bacteriologic conditions in the caverns, sanitarium, out of doors, and 

 in neighboring homes. My plates were prepared by being wrapped in 

 separate paper covers, sterilized in dry heat and transferred to a box 

 still wrapped in their paper covers. The agar-agar was in separate 

 tubes stoppered as usual with cotton plugs. Each morning before 

 starting in quest of bacteria the required number of fresh plates were 

 prepared. That my technic was entirely satisfactory was demon- 

 strated by setting a closed control plate at each place where other plates 

 were exposed. The readings from the plates were made after incuba- 

 tion for twenty-four hours at 85 degrees P. On the first day the 

 exposures and results were as follows: 



1. In the caverns : Three plates in Vegetable Garden, 50 yards from 

 entrance; plates exposed five minutes and one hour and the control 

 plate were all negative. 



Three plates at Crystal Spring, 100 yards from entrance; on plate 

 exposed five minutes, two colonies; plate exposed 50 minutes, negative; 

 the control plate, negative. 



Three plates at Skeleton Gorge, 200 yards from entrance; 5 

 minutes, 35 minutes, and control, all negative. 



Three plates at Cathedral Eoom, 300 yards from entrance; 5 

 minutes, 30 minutes, and control, all negative. 



2. In the air passage between the cave and the house (see Fig. 1) 

 four plates were exposed for one half hour as follows: Plate 1, at the 

 mouth of the air shaft coming from the caverns. A; plate 2, in the 

 beginning of the long auxiliary condenser, D^ just beyond the fan; 

 plate 3, at the other end of the auxiliary condenser; plate 4, on the 

 floor of the plenmn, where the air rushes down from the condenser. 

 On none of these plates was there any growth. 



3. In the sanitarium three plates were exposed for respectively 5, 

 20 and 60 minutes in each of three rooms, viz., the library on the first 

 floor; a guest chamber on the second floor, not used for the previous 

 week; and in a bedroom on the second floor, in constant use. The 

 morning work had been done in this latter room one hour before my 

 plates were placed on the bed. One colony on the five-minute plate, 

 and three colonies on the 60-minute plate in this room, and two 

 colonies on the hour plate in the library were the only results from 

 these nine plates. 



