58 TYPES OF BRITISH PLANTS 
Leaving these indefinite creatures, we come to the great 
single-celled family, which includes the Bacteria. This 
group has only recently attracted attention, so lately that 
the ninth edition of the Lncyclopedia Britannica does 
not give an article on Bacteriology; but of late years 
a vast amount of attention has been devoted to them, for 
it is held that some of them are the cause of diseases, 
amongst them cholera, plague, and typhus fever. But 
it would be most unfair to their character to imagine 
that all of them are evil. Vinegar is formed by the 
active exertion of one kind of bacillus, and there are 
others known as the sulphur and iron Bacteria, which 
are busily employed in making compounds of sulphur 
and of iron for the roots of higher plants to take up. 
Then there is a second group which appears to be quite 
harmless. There are certain kinds always to be found in 
our own mouths and noses, others inside the body in the 
alimentary canal, in which they seem to do no damage 
whatever, and possibly may give us active assistance, 
though it has not yet been discovered in exactly what 
way. 
Then comes the third group, those that are known 
to produce disease. These are all single-celled and of 
various shapes. The fungus that produces diphtheria 
is round; that of cholera is a bent rod, called from its 
shape the “comma” bacillus. The plague bacillus is a 
straight rod, and another may be spiral. All multiply 
by simply dividing the cells, splitting again and again 
at the expense of the nourishment in the host. One 
new cell will in twenty minutes be ready to split again, 
and produce another; and as each goes on splitting you 
can see at what a fearful pace they may multiply in a 
man’s blood, if the condition happens to be exactly 
