24 
HOUSEHOLD BACTERIOLOGY . 
Relations 
to Oxygen 
be obtained by actual measurement, only by compari¬ 
son. Fig. 14 represents the largest bacterium known 
magnified six hundred diameters. One twenty-five 
thousandth of an inch is not an uncommon length for 
a bacterium. 
Bacillus 
Megatherium. 
(a and b) Individ¬ 
uals. 
(c and d) Two indi¬ 
viduals, each di¬ 
viding into halves. 
Yet, small as they are, they are heavier than air, 
and therefore settle out of it when 
it is still. 
It is estimated that in the space 
occupied by a grain of sugar there 
might be packed six hundred mil¬ 
lions and each bacterium be com¬ 
fortable. Compared with the bac¬ 
teria which may lodge there, the 
wrinkles in the skin of our hands 
are like ditches six or eight feet 
deep. No wonder that it is diffi- 
* cult to dislodge them by any ordi¬ 
nary washing. The surgeon has to resort to a strong 
soap, vigorous brushing, and the use of numerous 
bacterial poisons in addition to the ordinary washing, 
before he is sure that these valleys are not rich in the 
tiny plants that might bring suffering or death to his 
patient. 
Most of the bacteria require oxygen to breathe, as 
we do, but some can live without air. Some will ac¬ 
commodate themselves to any condition. Preferring 
much or little oxygen, they will, however, grow under 
the opposite condition, if they must. 
