DISEASES AND ENEMIES. 
541 
Confining our inquiry within the narrowest possible 
limits, we have to do with pathogenic micrococci and 
bacilli, the former being minute, globular bodies 
(D, Fig. 123), which, at intervals, become slightly 
elongated, and then show a compression at what may 
be called the waist, giving them the form known 
technically as the dumb-bell. The compression becomes 
more pronounced, until, by separation, two tiny globules 
are produced from the one ; each of these will, in 
turn, divide, and so multiplication may go on at an 
astonishing rate. Bacilli, on the contrary, are rod- 
shaped (B and C, Fig. 123) ; and if we could suppose a 
common ruler to elongate without increasing in thick- 
ness, and then, at a definite point, break into two, 
to again increase in each part in like manner, we 
should have a fair idea of the question. But some- 
times this increase in length is not accompanied 
by separation, so that a line of bacilli may be 
formed comparable to a long string of sausages; 
and such is denominated a leptothrix (C, Plate I.). 
Under certain conditions, however, the bacilli produce 
spores, or seeds (E, Fig. 122), which the micrococci 
never do ; while, in addition, bacilli are provided at 
their extremities with wondrously delicate filaments 
(B, Fig. 123), called flagella, which often defy detec- 
tion, and are never seen but by the most skilful use 
of the finest microscope. With these they strike the 
fluid containing them, and so swim, much as a fish 
does by the use of its fins. 
Taking a speck of the tenacious, coffee-coloured 
matter previously mentioned, and placing it upon a 
glass slip, adding water, and then a cover-glass (an 
