80 A DISEASE GARDEN 
A singie generation, which isto be considered as the time 
elapsing between two successive divisions is frequently only 
the fraction of an hour. In some species the individual may 
grow to maturity and reproduce in twenty minutes. The 
rate of multiplication thus hecomes enormous as time goes on. 
Dr. Ferdinand Cohn calculated both the rate and the 
weight of this multiplication and justified his computations, 
being far from idle play, as they made the immense work 
exe cuted by the Bacteria comprehensible to us. 
The following table is compiled from Cohn’s calculations : 
Pee aa | Number of Individuals. | Weight. 
i 1 | 0.000,000,000,004,243, 672 
or. 
24 16,500,000 | 0.000,4 grain—plus 
48 47,000,000,000,000 | one pound—plus 
78 —--— | 825 tons 
100,000,000,000,000,000,000, | A mass about the size of 
168 000,000,000,000,000,000,000, | the world. 
000,000,000 | 
Fortunately for us, long before the offspring reach far 
into the millions, their rate of multiplication is checked either 
by lack of food, or by the accumulation of their own secreted 
products which are poisonous to them. 
Size of Bacteria.— The standard by which this is gauged 
is the 
MICRON. 
Unit of measure in Micrometry. 
METRE 
Ten millionth (1-10,600,000th) of a quadrant of the 
Meridian. 
39.3704 inches, or 3 feet, 3 inches and 3 eighths. 
Centimetre, c.m. 
0.01 or 1-100th of a metre. 
0.393,7 or 2-5ths (nearly) of an inch. 
Millimetre, m.m. 
0.001 or 1-1009th cf a metre. 
0.039,37 or 1-25th (nearly) of an inch. 
MIGRON, plural microns, micra, symbol, p 
0.001 or 1-1000th of a millimetre. 
0.000,001 or 1-1,000,000th of a metre. 
0.000,039,37 or 1-25,400th of an inch 
