DESCRIPTION OF PLATES. 131 
Sometimes the cells resulting from this con- 
tinued division remain attached to each other, and 
form little chaplets, like strings of pearls. Again, 
complete division occurs, and the micrococci_ re- 
main separate, or are grouped together in little 
masses (zoUglea). 
Sometimes division by fission does not occur in 
one direction only, but first in one direction, and 
then ina plane at right angles to this. The re- 
sult is that the micrococci are arranged in groups 
of four, and not, as in the other case, in a right 
line, in chaplets. 
As multiplication occurs with great rapidity 
when the conditions are favorable as to nutriment 
and temperature, it is evident that a small number 
of micrococci may produce an enormous progeny 
within a short time. Thus, in the case of the mi- 
crococcus seen in Fig. 2, Plate II., the multiplica- 
tion is so rapid that a single drop of fluid containing 
the organism, introduced beneath the skin of a 
large and healthy rabbit, causes the blood to be 
invaded throughout within forty-eight hours by 
such a multitude, that the smallest smear of blood- 
serum spread upon a thin glass cover, and placed 
under the microscope, gives us such a view as we 
have in the photo-micrograph. 
Cohn, a distinguished German botanist who has 
given special attention to the study of the Bacteria, 
makes the following estimate : — 
“Let us suppose that a bacterium divides into 
two in the space of an hour, then into four at the 
end of the second hour, then into eight at the 
