128 



GENERAL BACTERIOLOGY 



hours at 130' 



c. Sterilize in the hot air sterilizer for 1 and 

 C. (sugar melts at a higher 

 temperature). 



d. Fasten the tube, 

 pointed end up, in a clamp, 

 remove the first cotton 

 plug and connect with an 

 aspirator (Fig. 26). 



e. Break off the pointed 

 end of the tube and draw a 

 measured quantity of air 

 through the sugar. 



SPECIAL DIRECTIONS. 

 a. Filter 50 liters of 



air - FIG. 26. Aspirator for 



ft. Dissolve SUgar in 10 filtering air. 



cc. of sterile water (water-blank) and make 

 FIG. 25. Apparatus f or fli- plates, using 1 cc. of the mixture. 



tering air through sugar. r , 



A, ready for sterilization; c. Incubate, count colonies as above and es- 



B, point broken off and at- . . 



tached to aspirator; a and timate the number of organisms per liter or air. 



6, cotton plugs; c, sugar; 



d, clamp; e, rubber tube. , __ 



KEFERENCES. A. 604; H. 477; L. & K. 

 392 ; M. & R. 123 ; McF. 230. 



EXERCISE 68. WATER ANALYSIS. 



COLLECTION. Water for analysis must be 

 collected in a sterile vessel. A test-tube or flask 

 may be used in the laboratory, but when the 

 collection is made outside a sterile glass-stop- 

 pered bottle should be used. In collecting, 

 special care should be taken to get a fair sample ; 

 if the water be in a reservoir, or the like, the 

 bottle should be filled below the surface to avoid 

 the scum and away from the bottom to avoid the 

 sediment. Fig. 27 shows a form of apparatus 

 used to take samples in deep water. If some 

 time must necessarily elapse between the collec- 

 tion of the sample and its examination it should 

 be packed in ice. Specially constructed shipping 

 cases are used in most laboratories. 



o 



FIG. 27. Russell's 

 Water Sampler, a, 

 test-tube from which 

 the air has been ex- 

 hausted; &, glass tube, 

 sealed; c, sinker; d, 

 weight to be dropped 

 at proper depth. 



