28 MORPHOLOGIC VARIATION 



growth, but when subcultured during the logarithmic growth phase, 

 they grow at once at the same rate as in the parent culture, while 

 after the resting phase has been reached in the parent culture, the 

 subcultures show slight or no growth during the first two hours. 



The previous history of the culture used for seeding apparently 

 has some influence upon the rate of growth or the form of the 

 growth curve. Tenfold states that transfer from one medium to 



5 7—- 



I' 



to 



Ix 

 So 



=F=f=f=f 



I I I I I I I I I I I I I I I I I I I 



15 20 25 



Hours. 



Fig. 6. Influence of Age Of Parent Culture on Initial 

 Growth Rates of Pneumococci. 

 From "The Latent Period in the Growth of Bacteria" by A. Chesney. 

 Reproduced through the courtesy of the Journal of Experimental Medicine. 

 (1916, 24, 387). 



another of different composition may give a longer lag, the organism 

 requiring a period for adaptation to the new environment, although 

 he presents no data of his own. I have had an occasion to test 

 this theory, having at hand two cultures of the colon bacillus de- 

 rived from the same parent culture which had been carried for over 

 five years continuously, one on ordinary nutrient agar, the other on 

 a "synthetic" medium composed of various salts and glycerine. 

 These were subcultured simultaneously into flasks of nutrient broth 

 and the above mentioned medium, taking care to keep the size 

 of the seedings approximately the same. While the growth rate was 

 somewhat higher in the case of the broth cultures, both strains 

 behaved approximately the same, and there was no appreciable 



