The term bacterium of course in strictness only refers to the rod-shaped varieties of the group, but as it has given the name bacteriology to the science which deals with the whole group, it is convenient to apply it to all the members of the latter, and to reserve the term bacillus for the rod-shaped varieties. Other general words, such as germ, microbe, microorganism, are often used as synonymous with bacterium, though, strictly, they include the smallest organisms of the animal kingdom.
