66 CULTURES OF BACTERIA. 
culture to be studied, and draw it over the surface 
of an agar- or gelatin-tube that has been solidified 
with a slanting surface. 
(2) Allow to grow as before, and examine from 
day to day. 
(3) Note: 
(2) What are the size and shape of the streak ? 
(6) What is the character of the margin ? 
(c) Is the growth abundant or scanty, flat or 
raised, opaque or transparent?! 
(2) What is the color, luster ? : 
(e) Has the color, consistence, or odor of the 
medium changed ? 
II. POTATO AND BLOOD-SERUM CULTURES. 
Stroke cultures are employed in using potato or 
blood-serum tubes. The methods of study are 
essentially the same as described for gelatin or 
agar cultures. 
IV. PLATE CULTURES. 
In making plate cultures the nutrient medium is 
liquefied and a very small portion of the culture to 
be studied mixed with it; it is then poured into 
sterile Petri dishes, solidified, and the colonies 
allowed to develop. By this method the bacteria 
are scattered through the medium, and the colonies 
that develop are the descendants of a single germ. 
This permits different species to be separated from 
a mixture in pure culture, and the peculiarities of 
1 For descriptive terms, see p. 70, ef seg. 
