132 LABORATORY EXERCISES IN BACTERIOLOGY. 



wide end toward the narrow portion. After introduction of the sugar the cotton 

 is replaced in the wide mouth of the tube, the appliance held in vertical position (wide 

 end up) and the sugar shaken into the narrow tube. It is now again baked for steriliza- 

 tion of the sugar for several hours at a temperature of 120 C. Held in the same 

 position, it is then carried into the atmosphere to be examined, and the lower end 

 attached to some form of suction apparatus, as a pair of siphon bottles (the capacity 

 of which is known), the stopper removed from the upper end of the tube, and the 

 siphonage started. After a definite amount of air has been drawn through the sugar 

 the cotton stopper is replaced, the tube disconnected from the suction apparatus, 

 and the tube held in a horizontal position and slightly shaken to throw the sugar 

 back into the wide part of the tube. This done, twenty-five cubic centimeters of 

 liquefied sterile gelatine are introduced into the expanded part of the tube by means 

 of a bent pipette, the tube being maintained in horizontal position. In this liquid 

 the sugar is soon dissolved, leaving the bacteria which were adherent scattered in the 

 medium. The medium is now distributed over the inner surface of the expanded 

 part of the apparatus in the same manner as in any rolled tube and solidified by contact 

 with cold. It is set aside at room temperature for development of the bacteria, from 

 each of which it is assumed a focus of growth or colony will form in due time. The 

 colonies are eventually counted, from the number of which and the known amount 

 of air drawn through the tube the degree of impurity of the atmosphere may be ap- 

 preciated. From the tube special colonies as desired are to be transferred by means 

 of the sterile platinum needle for further study as isolated or pure cultures, as described 

 in a future lesson. 



Hesse's Apparatus. This consists (Fig. 40 B~) of a large, straight glass tube from 

 thirty to forty centimeters in length and from four to five centimeters in diameter. 

 The ends of this tube should be provided with perforated rubber stoppers, into the 

 holes of which are fitted short lengths of appropriate narrow tube (in one end the 

 tube fitted in the stopper should have a comparatively large diameter, 1.5 to 2.5 

 centimeters, while that of the other end may be about 0.5 centimeter in diameter). The 

 large glass tube is sterilized in the oven in the usual manner, the rubber stoppers and 

 their fittings in disinfectant solution and rinsed in boiled water. As soon as ready 

 the stoppers are fitted into the'tube and sterile cotton plugs placed in the small tubes 

 in the stoppers. A suitable quantity of sterile gelatine (twenty-five to fifty cubic 

 centimeters) is now liquefied and introduced into the tube by means of a curved pipette, 

 the apparatus being held in a horizontal position, and distributed over the inner surface 

 and there solidified as in the preparation of Esmarch tubes. This done, the tube is 

 carried to the atmosphere to be examined, and the narrow fitted tube connected with 

 a suction apparatus (tube held in any position after gelatine is solidified), and the 

 cotton removed from the other end. The suction apparatus is now set in action and 

 a definite quantity of air drawn through the tube. It is supposed that the organisms 

 in the air, in their progress from one end to the other of the tube, are likely to come 

 in contact with the gelatine film and adhere to it. The cotton stopper is then adjusted, 

 the suction apparatus disconnected, and the tube removed to the laboratory for de- 

 velopment (at room temperature) of the bacteria which have been introduced. As 

 in the method above described, the resulting colonies are counted, the ascertained 

 number being accepted as indicating at least the same number of individual bacteria 

 to have been present in the amount of air drawn through the tube ; and special colonies 

 are to be removed by means of the sterilized platinum needle for isolation and further 

 study. 



