136 PHOTO-MICROGRAPHS. 
These rod-shaped, filiform, and spiral Bacteria 
belong to different genera from that under consid- 
eration, — Micrococcus, — and the limits of the 
present volume do not permit of any extended 
account being given of them in this place. They 
are all more or less elongated, and all multiply 
by transverse fission in a plane at right-angles 
to their long diameter. A number of species are 
also known to multiply by the formation of endo- 
genous spores. ‘These are simply little masses of 
protoplasm formed in the interior of the rods or fil- 
aments by the consolidation of a portion of the 
semi-fluid protoplasm of the parent organism. 
These spores are spherical or oval in shape, and 
when set free by the breaking-up of the cell-wall 
of the mother-cell, may be mistaken for micro- 
coccl. They refract light more strongly, however, 
on account of their denser structure; and when 
placed in a suitable “ culture-fluid,” they grow into 
rods like the parent form, instead of producing 
spheres by binary fission, as do the micrococci. 
Pathogenie nucrococci — that is to say, disease- 
producing micrococci— have been proved to be 
the cause of certain infectious diseases among the 
lower animals, and it seems probable that other 
species may be the cause of certain infectious 
and epidemic diseases which afflict the human 
race. A minute micrococcus is constantly found 
in the pus of small-pox pustules and in recent 
vaccine virus. The veritable cause of the infec- 
tive virulence of the material in which they are 
found is as yet not definitely settled ; and in the 
