110 BOTANY. 
Among the bacteria which are of especial interest to us are the fol- 
lowing: 
1. The bacterium of small-pox (Micrococcus vaccine), composed of 
minute globular cells, is now accepted as the cause of small-pox. 
That found in vaccine virus is a cultivated state, while that in small- 
pox is its virulent state. 
2. The bacterium of diphtheria (Micrococcus diphtheriticus), simi- 
lar to but smaller than the preceding, is present in the body when suf- 
fering from diphtheria, 
8, The bacterium of ordinary putrefaction (Bacterium termo, Fig. 
46, b) is composed of oblong cells. It is the cause or accompaniment 
of all ordinary decay of animal and vegetable substances, 
4. The bacterium of anthrax or splenic fever (Bacillus anthracis) 
is composed of cylindrical cells, which are motionless. It occurs in 
the blood of animals suffering from the diseases named. 
5. The bacterium of consumption (Bacillus tuberculosis), of very 
slender cylindrical, motionless cells, has recently been shown to occur 
in the lungs and air-passages of consumptive patients. 
6. The bacterium of leprosy (Bacillus lepre), of cells similar to the 
preceding but larger, is found in the tissues of those afflicted with 
leprosy. 
Practical Studies.—(a) Put a pinch of cut hay or any other similar 
vegetable substance into a glass of water; keep in a warm room for 
a couple of days, or until it becomes turbid (from the abundance of 
bacteria); examine a minute drop with the highest powers of the 
microscope for active bacteria. 
(5) Put a bit of fresh meat into water, and study the bacteria which 
will appear in it. Spiral forms like g, Fig. 46, may often be found 
in such a preparation. : 
(c) Examine the juices of decaying fruits, 
226. Yeast-Plants.—If a bit of yeast be placed upon a 
glass slip and carefully examined under high powers of the 
microscope, there will be seen a great many small roundish 
or oval cells, of a pale or whitish color. They have a cell- 
wall, but generally the nucleus is wanting or indistinct. 
These little cells are Yeast-plants, and bear the name of: 
Saccharomyces cerevisiz. 
227. They reproduce by a kind of fission, called budding. 
Each cell pushes out a little projection which grows larger 
