SUMMARY: Live rod-shaped bacteria incubated on a medium containing 3 % urea grow but do not divide. They thus become much longer than dead bacteria lying among them, and the numbers of each kind can easily be counted in an electron microscope. This urea method gives accurate results and has several advantages over colony-counting methods. The significance of various interesting differences in the. counts given by the two methods is discussed. Slope cultures at 18 hr. gave live counts of over 95 % by the urea method.
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