BACTBEIA AS LIVING CELLS 



495 



nite shaped cells. Thus, bacillus tuberculosis is the name 

 given to the particular bacterium which causes tubercu- 

 losis. In this name the bacillus refers 

 to the shape of the cell (bacillus = rod 

 shaped), while the second name indi- 

 cates the specific action of this form. 

 Similarly, stophylococcus pyogenes 

 means spherical cells producing pus 

 formation. Spirillum volutans means 

 corkscrew-shaped cells which whirl in 

 their motion through liquids, etc. 

 (See Fig. 230). 



Bacteria as living cells. — Bacteria 

 contain no chlorophyll (or green col- 

 oring matter) and, therefore, cannot 

 make starch. On this account they 

 must find their food ready made. 

 Living organisms which obtain their 

 food at the expense of other organ- 

 isms are called parasites, and the liv- 

 ing organisms upon which they live are called their hosts. 

 If, however, the source of food be no longer living, as was 

 the case of the chopped hay in the tube, the organism which 

 feeds upon it is called a saprophyte. Bacteria are all para- 

 sites or saprophytes. Those which take their food from 

 living cells, such as the diphtheria and consumption forrrs, 

 belong to the parasitic forms, while those which live upon 

 dead matter, such as dead animal or plant structures, 

 belong to the saprophytic forms. 



Like all living cells, bacteria take in food and oxygen, and 

 give out wastes. They are rendered inactive by cold and 

 the presence of certain chemicals, while most of them are 



Fig, 229 — Bacteria, highly 

 magnitied; a, the germ 

 of typhoid fever, stained 

 to show the cilia; h, a 

 spiral ciliated form; c, a 

 rod-shaped form, in 

 chains; d, a spherical 

 form. — a, b, from Eno- 

 LEB and Pbamtl. 



