FORMS OF BACTERIA 653 



volutans, and less easily, but with almost equal certainty, in the 

 majority of other forms, not excluding B. termo. 



The simplest forms in which Bacteria are found are as isolated 

 cells of round or ovate shape : these are known as Micrococci, and 

 must be distinguished from immature and developing monads of the 

 saprophytiq group. The fission by which micrococci multiply may 

 take place in one direction only, and if the resulting cells remain 

 attached they form diplococci. If fission again occurs in each of 

 these cells and is repeated again and again and the resulting cells 

 remain attached, they give rise> to beautiful chains, rosaries, or 

 streptococci. If fission occurs in" single cells in two directions 

 tetracocci are formed, and if in three directions packets of eight are 

 formed, or sarcina-cocci . 



The rod-like forms are found isolated and free, or in chains. 

 Formerly short rods were called Bacteria, and long rods Bacilli ; 

 but as the term bacteria is applied to the whole group of fission- 

 fungi, it is more usual now to avoid confusion by speaking of all rod 

 forms, independently of their length, as bacilli. Some which are 

 fusiform in appearance are known as Clostridia. 



The coiled rods or spiral forms are either (1) closely coiled, when 

 they are known as Spirillum and Spirochcrte (more threadlike) ; or 

 (2) those more openly coiled are known as Vibriones. 



There are also very elonyated filiform varieties known as Lepto- 

 t/</'i.>; and branched forms as streptothrix. In Beggiatoa the fila- 

 ments are fixed at one extremity and stretch the other free in 

 the surrounding fluid. 



Colin classified bacteria according to their shape, but Ray Lankester, 

 Zopf, and others have shown that several micro-organisms in their 

 life -cycle exhibit successively the shapes characteristic of the orders 

 of Cohn. These pleomorphic species may be illustrated by Beygiatoa 

 alba. 



In the refuse waters discharged from factories, especially the 

 sulphuretted effluents of sewage works, is found this form the 

 1 sewage fungus ' of engineers. It may have a thickness of 5//, and 

 it maybe as attenuated as to measure only lp. It is attached in an 

 erect manner to objects in the impure water it affects (fig. 487) ; and 

 the filaments consist of rows of cells, and in the protoplasm of these 

 granules of sulphur are enclosed. The filaments readily break up 

 into cells about as long as they are broad, and become at length 

 active but eventually attach themselves to some object and come to 

 rest, when they multiply by fission and accumulate in masses of 

 zooylcca. ' They may develop into rods, and these again into the 

 filaments after the rods have passed through the swarming state.' 



Spirally twisted forms also arise in this species. These break 

 into coiled parts, possessed of flagella, and exhibit extremely active 

 movement. The flagella in these are as strong and easily seen as 

 in the Spirillum volutans, and these forms were known at an earlier 

 period as Ophidomonas. 



Fig. 487 shows at 1 a group of the attached filaments of Beggiatoa 

 alba : 2 to 5 show portions of filaments of differing diameters ; 5 

 shows a filament in the act of multipartition. The small dark circles 



