11 
11. Examine a dark-field preparation of carmine particles. See the instruc¬ 
tor’s demonstration. 
12. Great numbers of bacteria of different kinds will develop in a jar 
containing water and grass, hay or leaves, etc. The soluble substances in these 
diffuse into the water and serve as food for bacteria and other micro-organ¬ 
isms. The micro-organisms that were on the hay and leaves, in the water or 
adhering to the jar or those that are introduced with dust from the air develop 
with amazing rapidity. This development will take place at temperatures 
varying from 15 degrees G. to 40 degrees C. and is an example of what is 
taking place in nature wherever food and moisture permit the growth of 
bacteria. 
Prepare a hanging drop from the infusion on the desk and locate the drop in 
the same way as before. 
13. After locating the edge of the drop with the 16 m. m. objective, examine 
it with the 4 m. m. objective. Focus upward very slowly with the fine adjust¬ 
ment until the objects are in view. The organisms in the shoal water are the 
most easily studied. The large, round, oval and oblong objects that seem to 
move about so rapidly are not bacteria, but animals. Animals like these are 
known as protoza. The small, round, rod, or spiral-shaped individuals 
present are the bacteria. 
14. Draw and describe afield as seen in the hanging-drop preparation. 
(a) Are there a number of kinds of bacteria in the infusion? Give 
reasons for your answer. 
(b) Can any of them move? Indicate the path of the movement 
of individual organisms by dotted lines and arrows. 
(c) What seems to be the nature of their movement? Notice the 
apparent vibration of some of them that are not moving from 
place to place. 
15. Examine in hanging drop each of the pure cultures of bacteria furnished; 
draw and describe each. 
16. From the observations of the cultures, classify each one according to 
shape. (See Fig. 5). 
(a) Unstained, living bacteria have been examined as well as 
stained, dead bacteria. Which one of these preparations is 
the easier to study? Why? 
( b ) Can flagella be seen on the bacteria in any of the preparations 
Give the reason for your answer. 
(c) Can dead bacteria be detected by observation of a hanging 
drop? Give reasons for your answer. 
