4 MANUAL OF BACTERIOLOGY. 



I. The lower bacteria include these forms which are of most 

 importance at present, and consist of — ■ 



Micrococci, or cocci (singular, coccus) — spherical forms. 



Bacilli (sing., bacillus)— long and straight, or rod-shaped 

 bacteria. 



Spirilla (sing., spirillum) — consisting of spiral filaments hke 

 the turns of a corkscrew, or parts of spirals shaped like commas. 



II. The higher bacteria, which con- 



«•%■? -.^S5•*I ^^ ^^^*- °^ ^°^S filaments made up of 



*■■ '• ' ^ ^ \ ,1 1^ J segments more or less united. In 

 Micrococci. Bacilli. Spirilla. somc of thesc thc^ filaments show 

 Pjq j dichotomous branching. This group 



is more fully discussed under the 

 non-pathogenic bacteria, Part III. A few of them are patho- 

 genic. 



The extreme smallness of the bacteria is hard of compre- 

 hension. We may say, of most of them, that from 5,000 to 25,- 

 000 placed end to end would make a line about an inch in length. 

 When one touches a growth of bacteria with the sterilized 

 platinum wire and spreads the tiny portion that adheres to the 

 wire upon a slip of glass, it is found upon examination with the 

 microscope that the bacteria left on the glass may be compared 

 to the stars in the sky, the grains of sand on the shore, or any of 

 the other standards for numbers that are nearly beyond com- 

 putation. 



It is well known that bacteria are present on mcst of the 

 objects about us. They occur on the skins of men and other 

 animals, as well as in the mouth, stomach and intestines, and 

 on most of the surfaces of the body that open to the external 

 world. They are found in the water of rivers and lakes, and in 

 the ocean. They appear in the soil down to a depth of several 

 feet. They float in the air, except at high altitudes and over 

 the ocean. Nansen found bacteria on the ice of the Polar sea. 

 Investigators have even reported finding them fossilized, indicat- 



