STEUCTUEE OF MICEO-OEGANISMS 7 



results of individual experiments into a statement of 

 general law. This error is as dangerous as it is hard to 

 avoid ; and the effort to avoid it is the first and not the 

 least important duty of a student of bacteriology. The 

 results so far obtaiued, however, are so important that it 

 has become an absolute necessity for those concerned in 

 the study and treatment of disease to have some know- 

 ledge of this branch of science. But enough has been 

 said to pave the way for the better appreciation of the 

 marvellous manner in which these investigations have led 

 and are leading to the most important and far-reaching 

 results in medicine. 



Structure of Micro-organisms. — The bacteria appear under 

 the microscope as pale, translucent bodies ; they consist of 

 unicellular organisms composed of protoplasm surrounded 

 with a membrane, or skin, of a body allied to cellulose.. 

 This outer skin swells up in some cases to form a jelly-lika 

 casing, by which the internal protoplasm is covered. 



The cells sometimes contain a nucleus which is readily 

 stained with the usual staining reagents. 



Types of Organisms. — The organisms vary very much in 

 shape and size. Many are globular or spherical in shape, 

 and are generally known as micrococci ; others, on the other 

 hand, are rod-like bodies, hence are termed bacilli ; whilst 

 others, having a spiral or corkscrew shape, are known 

 as spirilla. Some spirilla sometimes appear in a much 

 shorter form, and resemble the shape of a comma. Very 

 short rodlets are often known as bacteria — if fairly long, 

 as bacilla; very long filaments are included under the 

 name Leptothrix. Other kinds branch, and are known by 

 the name of Cladothrix. 



All these various shaped organisms are loosely spoken 

 of as bacteria. In addition to these forms are two other 

 classes of micro-organisms, namely, the moulds and 



