THE EATE OF REPRODUCTION. 59 



as ascertained by BUCHNER, LONQARD, and RIEDLIN (I.). If the 

 number of cells present in a bacterium culture at the commence- 

 ment of an experiment be represented by a, and at the end of a 

 given time, t, has increased to b ; then, according to FR. BASENAU 

 (L), the period of generation is 



t log 2. 

 x ~~ log b - log a. 



Cohn, starting with the assumption that the period of gene- 

 ration is half-an-hour, made the following calculation. If we 

 take a single bacillus measuring 2 ^ in length and i ^ in breadth, 

 with a weight of 0.000000001571 mgrrn., it will increase, according 

 to the aforesaid assumption, at such a rate that in two days' time 

 its progeny will amount to 281 billions, and will occupy a volume 

 equal to about half a litre (30.51 cub. ins.). Within a further 

 three days, the quantity would increase to a mass sufficient to 

 completely fill the beds of all the oceans on the globe, and the 

 number of the progeny would be expressible only by 37 places of 

 figures ! That such an inordinate development does not occur is 

 mainly owing to the repressing effect of external influences, and 

 especially to the enmity existing between the various species them- 

 selves. A no less powerful and inevitable retardation is caused 

 by the transformation products excreted as a result of the vital 

 activity of the reproducing cells, which finally arrest further growth, 

 even though a sufficiency of nutriment is still available. 



