C.-E. A. WINSLOW 59 



scription of the lag phase in a favorable medium were due to Miiller (1895) who intro- 

 duced the now-familiar formula for generation time: 



log 6— logo 



where G= minutes per generation, r = elapsed time in minutes, a = initial number of 

 bacteria, and 6 = final number of bacteria. 



He showed that G increased with the age of the primary culture used for inocu- 

 lating the medium in which generation time was measured. Thus typhoid bacilli inoc- 

 ulated from a 2.5-3-hour mother-culture gave a generation time of 40 minutes while 



Fig. I. — Ideal curve of a bacterial population cycle. Ordinates = numbers; abscissae = elapsed 

 time. 



A-B. Phase of adjustment D-E. Phase of decrease 



B-C. Phase of increase E-F. Phase of readjustment 



C-D. Phase of crisis 



those from a 6j-hour culture completed a generation in 80-85 minutes, and those from 

 a 14-16-hour culture in over 160 minutes. He attributed the slower generation in 

 media inoculated from older cultures to what is now called a "lag effect." Hehewerth 

 (1901) confirmed these results. It was Rahn (1906), however, who first studied the 

 preliminary lag period intensively, using B. fliwrescens in broth. 



He inoculated from (I) 20-hour broth, from (II) 20-hour agar, and from (III) 4- 

 month broth, and obtained such results as are shown in Table I. 



If the medium be less favorable, the phase of adjustment will be marked by a de- 

 crease followed by an.increase. This latter phenomenon was noted at least as early as 

 1894 (Fuller, 1895) in studies made at the Lawrence Experiment Station of the Massa- 

 chusetts State Board of Health which showed that a bottled sample of sewage orig- 

 inally containing 1,190,000 bacteria per cubic centimeter fell off to 1,085,000 after 2.5 

 hours, then rose steadily to a maximum of 23,100,000 after 25.5 hours, and then fell 



