SPECIAL EXAMINATIONS 363 



and then permanent alkalinity, and glucose and mannite, 

 in both of which it produces acid only, may be considered 

 to be Bacillus typhosus. It should then be tried for 

 agglutination in high dilutions of anti- typhoid serum. 

 Pfeiffer's reaction may also be tried with a known immune 

 serum. (See p. 191.) 



VII. Isolation of Spirillum Cholerae. This has 

 already been described on p. 324. 



Summary of Some Results : see preceding page. 



BACTERIOLOGICAL EXAMINATION OF AIR. 



Various methods are employed : 



1. Exposure of Plates for a Definite Time. Incubate ; 

 enumerate ; identify. 



2. Hesse's Method. A glass cylinder, 18" X 2", is closed 

 at one end by an indiarubber cover, tightly adjusted. 

 The other end is stopped with a close-fitting rubber cork, 

 through which passes a glass tube, attached by rubber 

 tubing to a litre flask filled with water, and which, in its 

 turn, is similarly attached to another litre flask, empty and 

 having its outlet tube clamped. Along the bottom of the 

 cylinder, 50 c.c. of nutrient gelatin are spread, or may be 

 rolled all over the inside of tube. The whole is rested on a 

 tripod stand. Sterilize in the usual way and keep to see if 

 sterile. To test air : pierce a small hole in rubber cover, 

 and open pinchcock on empty litre flask, which place lower 

 than other. Water begins to run from the upper flask to 

 the lower, and aspirates air through the pierced hole over 

 gelatin. By reversing the flasks, another litre of air can 

 be aspirated, and so on. Finally, detach the tubing from 

 cylinder, cover the ends with sterile wool, and incubate for 

 twenty-four hours onwards. 



This method has been largely superseded by simpler ones. 

 All the microbes may not be caught on the gelatin surface. 



3. Frankland's Method. A tube, 5" X J", containing 

 two plugs of glass wool. Aspirate a known quantity of 

 air, remove the wool, and add to nutrient gelatin, and plate. 

 The glass wool mixes with the gelatin. 



4. Petri's Method. Like Frankland's, only using sand 

 instead of glass wool. There is apt to be some difficulty 

 in distinguishing between colonies and grains of sand. 



