250 BACTERIOLOGY. 



temperatures some forms of bacteria increase rapidly. 

 Unless the nutrient gelatin or agar inoculations are 

 made within an hour or two the count of the number 

 of colonies is practically useless. Considerable care 

 is necessary in taking the samples of water, so as not 

 to get extraneous organisms in the water from sur- 

 rounding sources. Three slightly different methods 

 will suffice to indicate how it should be done. A 

 simple and accurate method of collecting the water is 

 to have several graduated sterile glass pipettes plugged 



FIG. 35. FIG. 36. FIG. 37. 



Bulb pipette. Graduated pipette. Sternberg bulb. 



at the bottom by a cork and above by cotton. This is 

 inserted the required depth, to avoid the surface water 

 with its particles of dirt, and the cork pushed off by 

 a second pipette or rod and the water allowed to flow 

 or be sucked in. The upper end is now stopped by 

 the finger and the pipette removed and a definite 

 amount of water tested (Figs. 35 and 36). A simple 

 glass tube, sterilized by passing it through a flame and 

 corked below, will answer the same purpose, or, again, 

 a tube, one end of which, after sealing, is blown into a 

 sphere and the other end drawn out into a capillary stem 



