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 
Fie. 35. Fie. 36. Fie. 37. 
it] 
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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 
