THE RATE OF REPRODUCTION 45 



be represented by a, and at the end of a given time, 2, has increased to b; then, 

 according to Fn. BASENAU (I.), the period of generation is 



t lojr 2 



log b lojr ' 



Cohn, starting with tlic assumption that the period of generation is half an 

 hour, made the following calculation. If we take a single bacillus measui-inir 

 2 p in length and i /* in breadth, with a weight of 0.000000001571 mgrm., 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 farther three days the 

 quantity would increase to a mass sufficient to completely fill the beds of all \]\c 

 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 themselves. 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. 



