110 BOTANY. 



Among the bacteria which are of especial interest to us are the fol- 

 lowing: 



1. The bacterium of small-pox (Micrococcus vaccinse), 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 diplitheriticus), simi- 

 lar to but smaller than the preceding, is present in the body when suf- 

 fering from diphtheria. 



3. 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 o£ animaK suffering from tlie 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 lepiosy (Bacillus leprse), of cells similar to the 

 preceding but larger, is found in the tissues of those afflicted with 

 leprosy. 



l^actical Studies. — (a) Put a pinch of cut hay or any other similar 

 vegetable substance into a glass of water; lieep in a warm room for 

 a couple of days, or until it becomes turbid (from tlie abundance of 

 bacteria); examine a minute drop with the highest powers of the 

 microscope for active bacteria. 



(J) 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. 



(fi) 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 cerevisise. 



227. They reproduce by a kind of fission, called budding. 

 Each cell pushes out a little projection which grows larger 



