14 MANUAL OF BACTERIOLOGY. 



and, on the other hand, they have strong points of likeness 

 with some of the unicellular animals belonging to the in- 

 fusoria. 



Bacteria are divided into three great groups : 



Micrococci, or cocci 1 (singular, coccus) spherical forms. 



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

 bacteria. 



Spirilla (sing., spirillum) consisting of spiral filaments 

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

 like commas. 



The extreme smallness of the bacteria is hard of com- 

 prehension. 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 



K? ^^\l " /N T / " with the sterilized platinum wire 

 v \ .j* 



' ^ % ^ (j r j anc { spreads the tiny portion 



Micrococci. Bacilli. Spirilla. that adheres to the wire upon a 



slip of glass, it is found upon ex- 

 amination 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 computation. 



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

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

 other animals, as well as in the mouth, stomach and intes- 

 tines, and on most of the surfaces of the body that open 

 to the external w^orld. 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 



1 Pronounced kok-si or kok-ke : see Webster's International, Century, 

 and Standard Dictionaries, and Foster's and Keating's Medical Diction- 

 aries. The writer knows of no authority for the prevailing pronuncia- 

 tion kok-kl. 



