The Story of Germ Life | Page 7

convenient one to retain although the bodies in question are not
true spores.
Still a different method of spore formation occurs in a few peculiar
bacteria. In this case (Fig. 14) the protoplasm in the large thread breaks
into many minute spherical bodies, which finally find exit. The spores
thus formed may not be all alike, differences in size being noticed. This
method of spore formation occurs only in a few special forms of

bacteria.
The matter of spore formation serves as one of the points for
distinguishing species. Some species do not form spores, at least under
any of the conditions in which they have been studied. Others form
them readily in almost any condition, and others again only under
special conditions which are adverse to their life. The method of spore
formation is always uniform for any single species. Whatever be the
method of the formation of the spore, its purpose in the life of the
bacterium is always the same. It serves as a means of keeping the
species alive under conditions of adversity. Its power of resisting heat
or drying enables it to live where the ordinary active forms would be
speedily killed. Some of these spores are capable of resisting a heat of
180 degrees C. (360 degrees F.) for a short time, and boiling water they
can resist for a long time. Such spores when subsequently placed under
favourable conditions will germinate and start bacterial activity anew.
MOTION.
Some species of bacteria have the power of active motion, and may be
seen darting rapidly to and fro in the liquid in which they are growing.
This motion is produced by flagella which protrude from the body.
These flagella (Fig. 15) arise from a membrane surrounding the
bacterium, but have an intimate connection with the protoplasmic
content. Their distribution is different in different species of bacteria.
Some species have a single flagellum at one end (Fig. 15 a). Others
have one at each end (Fig. 15 b). Others, again, have, at least just
before dividing, a bunch at one or both ends (Fig. 15 c and d), while
others, again, have many flagella distributed all over the body in dense
profusion (Fig. 15 e). These flagella keep up a lashing to and fro in the
liquid, and the lashing serves to propel the bacteria through the liquid.
INTERNAL STRUCTURE.
It is hardly possible to say much about the structure of the bacteria
beyond the description of their external forms. With all the variations in
detail mentioned, they are extraordinarily simple, and about all that can
be seen is their external shape. Of course, they have some internal

structure, but we know very little in regard to it. Some microscopists
have described certain appearances which they think indicate internal
structure. Fig. 16 shows some of these appearances. The matter is as yet
very obscure, however. The bacteria appear to have a membranous
covering which sometimes is of a cellulose nature. Within it is
protoplasm which shows various uncertain appearances. Some
microscopists have thought they could find a nucleus, and have
regarded bacteria as cells with inclosed nucleii (Figs. 10 a and 15 f).
Others have regarded the whole bacterium as a nucleus without any
protoplasm, while others, again, have concluded that the discerned
internal structure is nothing except an appearance presented by the
physical arrangement of the protoplasm. While we may believe that
they have some internal structure, we must recognise that as yet
microscopists have not been able to make it out. In short, the bacteria
after two centuries of study appear to us about as they did at first. They
must still be described as minute spheres, rods, or spirals, with no
further discernible structure, sometimes motile and sometimes
stationary, sometimes producing spores and sometimes not, and
multiplying universally by binary fission. With all the development of
the modern microscope we can hardly say more than this. Our advance
in knowledge of bacteria is connected almost wholly with their
methods of growth and the effects they produce in Nature.
ANIMALS OR PLANTS?
There has been in the past not a little question as to whether bacteria
should be rightly classed with plants or with animals. They certainly
have characters which ally them with both. Their very common power
of active independent motion and their common habit of living upon
complex bodies for foods are animal characters, and have lent force to
the suggestion that they are true animals. But their general form, their
method of growth and formation of threads, and their method of spore
formation are quite plantlike. Their general form is very similar to a
group of low green plants known as Oscillaria. Fig. 17 shows a group
of these Oscillariae, and the similarity of this to some of the thread-like
bacteria is decided.