94 MICRO-ORGANISMS IN RELATION TO MAN, 
with other characteristics, are divided into various classes. 
Thus, some are simply more or less spherical granules, to 
which are given the name Micrococci (Fig. 6); others again 
with longer and shorter rod-like form, are known as Bacilli 
(Fig. 4); whilst others, having a corkscrew or spiral form, 
receive the name of Spirilla. The members of the last 
mentioned class sometimes appear in a shorter and dis- 
jointed form, and then resemble a ‘“‘ comma” (Fig. 5.) Some- 
times the individual cells terminate in long, highly attenuated, 
hair-like processes, which are generally seen in a state of 
great agitation and serve as a means of propelling the bac- 
terlum through the liquid in which it exists. 
Bacteria multiply in two ways. The more usual way is 
by the simple process of cell-division—a transverse partition 
forms in the centre of the adult organism, which then divides 
into two portions. Under favourable conditions this process 
takes place with extreme rapidity, and it has been estimated 
that in 72 hours there would be produced from one cell the 
enormous number of 4,772 billion organisms. This mode of 
splitting up transversely to their length has led to the term 
‘‘ fission-fungi” being given to the micro-organisms of this 
group. The second mode of multiplication is not nearly so 
frequent, but is in many respects more important. When 
certain species of bacteria are placed under conditions un- 
favourable to their free development, there is formed in the 
interior of the cells one or more round or oval bodies, having 
a very bright and refractive appearance. These bodies are 
known as spores (Fig. 3) and from their powers of resistance 
to outside influences, they play a most important part in the 
propagation of many organisms. In many cases they will 
survive the application of the most intense cold it is possible 
to produce; the spores of many species will also develop 
after the liquid containing them has been boiled for some 
time; they will also withstand the action of antiseptics— 
both as regards strength and duration of action—for a much 
