Page:Popular Science Monthly Volume 64.djvu/563

Rh 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; i. 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 demonstrated by setting a closed control plate at each place where other plates were exposed. The readings from the plates were made after incubation for twenty-four hours at 85 degrees F. 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 Room, 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 plenum, 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.