MORPHOLOGY ee 
EXERCISE XIV 
THE MORPHOLOGY OF STREPTOCOCCUS, MICROCOCCUS, 
AND SARCINA 
83. Genera among bacteria are based on the gross mor- 
phology of the organisms. This is very largely true of all clas- 
sifications. It is highly important, therefore, that the generic 
characters should be thoroughly learned. While the descrip- 
tive differences between a micrococcus and a bacterium seem 
to be clear, there are many organisms where it is not so easy 
to decide in which genus to place them. The almost constant 
appearance of unexpected bacteria in septic infections and 
in diseased organs renders it exceedingly desirable that one 
should understand the fundamental elements of classification. 
We must remember that the problems of the practitioner are 
not all centered about known pathogenic forms like the organ- 
isms of tuberculosis and diphtheria, but they have to do with 
a great host of infecting bacteria of which we know as yet but 
very little. 
84. Work for this exercise. Carefully describe each of the 
cultures made in Exercise XIII. <7 
Prepare and examine a hanging-drop preparation from 
each of the cultures, and describe the appearance (form) 
of the organisms in each. Indicate the morphologic charac- 
ters by which each genus can be differentiated from the 
others. 
Make a cover-glass preparation from each culture and stain 
with an aqueous solution of methyl violet (§ 38). Make 
a careful microscopic examination of each preparation and 
describe the bacteria in each. 
Make careful notes on the appearance of the bacteria in each 
preparation and preserve a specimen of each to accompany 
the notes. 
