50 ' JOURNAL OF SCIENCE, 
means of course that an army of twenty thousand strong could 
stand side by side in a single row within the space of one linear 
inch, In this diagram I have half a Bacterium magnified 300,000 
diameters, the length of the body being made 18 inches, its 
breadth 15 inches, or thereabouts. 300,000 Bacteria—about 500 
times the population of Oamaru—would lie side by side along 
the diameter of the figure, 43,260 millions would lie closely 
packed in one layer on its surface, and if instead of a flat dia- 
gram we had a hollow model, it would contain no less than 8823 
millions of millions.* I mention these figures in order to give 
you some slight idea of the almost infinite minuteness of these 
little beings. 
There is one other point which can only be made out by the 
very highest powers of the microscope, and even then only with 
very skilful management :—To each end of the spindle-shaped 
body is attached an extremely delicate transparent thread, rather 
longer than the body, and so fine that its diameter at the thickest 
part does not exceed the one two-hundred-thousandth ofan inch. 
While the Bacterium is alive this cz/zm is in constant lashing 
motion, and it is by its means that the creature is propelled 
through the water. 
During the earlier stages of putrefaction these little spindle- 
shaped bodies—which are distinguished by the name Bacterium 
termo—are the only organisms found, but later on we always find 
much larger Bacteria having a rod-like form with a cilium at each 
end, and distinguished by the name Lacillus. There are also 
found curved rods called Vzdvz0, and in many putrefying in- 
fusions occur larger rods coiled into a perfect spiral and called 
Spirillum: these last are the giants among Bacteria, some of 
them being fully one-thousandth of an inch in length. All these 
are grouped under the common name Lacterza. 
Chemical examination, the details of which I cannot go into, 
shows that bacteria are composed of a complex substance called 
Protoplasm, made up of bodies known to chemists as Proteids, a 
group of organic substances which includes albumen or white of 
egg, the casein of cheese, the gluten of wheat, etc. One property 
of protoplasm is that it stains rapidly with certain colouring 
matters such as ordinary aniline dyes, so that Bacteria treated 
with a dye like magenta, aniline-violet, etc, become very con- 
spicuous objects under the microscope. Of course such treatment 
immediately kills them. |Probably—almost certainly—the pro- 
toplasm is surrounded by an extremely thin layer of a substance 
called ce//ulose—the elementary form of woody tissue—but under 
ordinary circumstances the presence of this covering is only sur- 
mised from analogy and cannot be actually demonstrated. 
Now if a bit of one of the higher plants—say of a leaf—is 
examined microscopically, it is found to consist of small masses 
of protoplasm each enclosed in a wall of cellulose and called a 
cell; and a bit of one of the higher animals—say of our own skin 
* Professor Shand was good enough to make these calculations for me, 
