VIABLE BACTERIA IN YOUNG CULTURES 



441 



to live and divide, while 20 per eent failed to do so, the result 

 would be that at the end of the logarithmic phase the total num- 

 ber of organisms alive and dead would exceed the number of 

 li\'ing organisms. Further, the increase in the living organisms 

 would still occur by geometrical progression, and the resultant 

 curve of plotting the logarithms of the numbers would still fall 

 on a straight line ; the only difference would be that instead of the 

 number of organisms being doubled in each generation, they 

 would only be increased 1.6 times as much. To make this clear, 

 suppose there are 1000 organisms per cubic centimeter, alive at 

 the commencement of the logaritlmiic phase. At the end of the 

 first generation there would be 2000 organisms, of which 80 per 

 cent or 1600 would Uve and divide, while 20 per cent or 400 would 



TABLE 23 



At start 



At end of first generation 



At end of second generation. 

 At end of third generation... 



NUMBER OF VIABLE 



ORGANISMS PER 

 CUBIC CENTIMETER 



1,000 

 1,600 

 2,560 

 4,096 



NUMBER OF DEAD 



ORGANISMS PER 



CUBIC CENTIMETER 







400 



640 



1,024 



TOTAL NUMBER OF 



ORGANISMS PER 

 CUBIC CENTlMtTKR 



1,000 

 2,000 

 3,200 

 5,120 



die. In the next generation these 1600 would divide and produce 

 3200 organisms of which again 20 per cent or 640 would die, 

 while 2560 would Uve and divide and so on. In tabular form it 

 may be seen more clearly still. 



It will be noticed that the Uving organisms increase in each 

 generation by 1.6 times as many as those present at the com- 

 mencement. On the other hand the factors of increase for both 

 dead and total organisms start high and gradually decrease 

 till after several generations they approximate to 1.6. If curves 

 were plotted of the logarithms of these counts, it would be seen 

 that the curve for the viable organisms would he along an as- 

 cending oblique straight line, whereas that for the total would 

 rise at first rapidly and then gradually become flatter till it ran 

 almost parallel to that for the viable count. Whether this is so 

 in practice cannot be ascertained, as no practicable method of 

 counting total numbers of organisms during the early part of the 



