30 
If we take a small quantity of hay, for convenience, divided 
into small pieces, and pour sufficient boiling water on it to cover 
it, infuse for half an hour, and then filter, we shall obtain a 
perfectly clear fluid, which, in the course of a day or two will 
become turbid, and on the surface of which a scum will form later 
on; at the same time the infusion will have acquired a marked 
putrefactive odour. If we now take a drop of the solution and 
examine it under a high power of the microscope, we shall find it 
swarming with elliptical or rod-like or jointed bodies in active 
motion. These are the moving bacteria. An examination of the 
scum shows the bacteria in their resting stage. Mixed with the 
bacteria proper, both in the pellicle and the fluid beneath, we may 
find a number of forms of living beings. 
The question arises whether the bacterium is an animal or 
a plant. It has a continuous cell-wall, and the power of forming 
a protein from inorganic matter, such as ammonium tartrate, which 
are distinctly vegetable characteristics. On account of its absorb- 
ing oxygen and giving off carbonic acid, and on account of its 
power of motion, it has been placed by many naturalists in the 
animal kingdom. But the whole group of fungi—plants which 
contain neither chlorophyll nor starch—absorb oxygen and give off 
carbonic acid, and many of the lower plants, especially in the 
group of Ales, give rise, under certain circumstances, to locomotive 
bodies propelled by~cilia. On the power which bacteria possess 
of seizing on the nitrogen of organic matter and appropriating it 
in the building up of their own proto-plasm, probably depends their 
power of exciting putrefaction. They have their place in nature 
as the universal destroyers of nitrogenous substances ; they appro- 
priate, for their own growth, the nitrogen which they steal. ‘The 
germs of Torula are abundantly present in the air. In all 
fermentible liquids exposed to the air fermentation ensues sooner 
or later from the access of these germs. On the other hand the 
germs of bacteria, as Dr. Burdon Sanderson’s experiments show, 
are not present in the air, but are abundant in water and on all 
surfaces not chemically clean. They exist in the purest waters, 
even in distilled water (unless very special care has been taken in 
its prepartion to exclude all possible source of contamination), and 
on the surfaces of all vessels, 
Bacteria are not only interesting as natural objects and as the 
universal exciters of putrefaction, but they derive additional interest 
from their close association with certain forms of disease in the 
higher animals. It has been shown that in acute infective inflam- 
mation microzymes abound in the exudation liquids, and that the same 
forms are also to be found in the blood of the infected animals, 
their presence being a constant accompaniment of all acute infective 
