494: BACTEEIA AND SANITATION 



The milk gradually curdles and becomes sour to the 

 smell and taste. 



The meat gives off fetid odors and changes in color 

 and appearance. 



If, now, we mount some of the liquid from any one of 

 these three tubes on a slide under a compound microscope, 

 we find it swarming with curious-shaped little bodies myriad 

 in number and with sharply defined outlines. These bodies 

 are extremely small beings, only ^^-q-^ to -g-oiTo of an inch 

 in diameter. Examined with the highest powers of the 

 microscope they are seen to consist of a cell waU sur- 

 rounding a bit of protoplasm, while scattered through 

 the protoplasm are tiny particles which color more strongly 

 than the other parts, when stained, and are supposed to 

 correspond to the nuclear material of other cells. These 

 tiny bodies are bacteria. 



Definition and forms of bacteria. — Study of preparations 

 such as the above, and of other sources, shows that there are 

 many different species of bacteria, all differing in shape and 

 action, but aU showing the characteristic waU of cellulose 

 and the scattered nuclear material. It is this cellulose wall 

 that inclines us to place these forms among the plants. We 

 can, therefore, define bacteria as follows : One-celled vege- 

 table organisms having a definite .unchanging cell wall and 

 containing nuclear material in the form of scattered frag- 

 ments which is never combined in the form of a single 

 nucleus. Certain forms show cilia and are capable of move- 

 ment. Others move only as they are carried about by the 

 air or liquids in which they are present. 



In identifying and naming bacteria, use is made of the 

 unvarying character of the outline. Experience has also 

 shown that definite actions are always associated with defi- 



