22 BACTERIOLOGY. 



form can be reproduced whenever the organism is trans- 

 planted and grows under its most favorable conditions of 

 soil and temperature. 



The methods of examination may apparently influence 

 the form of a given species. This is very often seen in 

 stained preparations. As a result of heavy staining, such 

 as is resorted to in order to demonstrate flagella, the 

 organism appears much larger and thicker than when 

 stained in the ordinary way. The successive deposition of 

 the dye, layer on layer, causes an apparent increase in the 

 size of the cell. Again, in the method of double- staining 

 tubercle and leprosy bacilli, the bacteria, after being heavily 

 stained, are partly decolored with alcohol. Depending 

 upon the extent of the decoloration, they may appear as 

 relatively thick or as extremely thin rods. 



As a rule the bacteria present in tissues, when stained, 

 appear smaller and narrower than in the fresh material. 

 This variation is in part due to the contraction of the pro- 

 toplasm or contents of the cell by the alcohol employed to 

 harden the tissue. It is also due to partial decoloration 

 which is unavoidable when the bacteria are to be differen- 

 tiated from the tissue in which they lie imbedded. 



As a result of the action of various chemical substances 

 the protoplasm of the bacterial cell may be contracted or 

 drawn up into irregular masses or granules. When such 

 forms are stained they may appear like minute micrococci, 

 although the original form was that of a typical rod. This 

 action on protoplasm is designated as plasmolysis. Expos- 

 ure of bacteria to iodine is likely to result in plasmolytic 

 changes. Similar alterations are met with as the result of 

 overheating specimens in the process of preparation (Fig. 4). 



From what has been said above with reference to 

 variation in the form of a given species, it is evident that 

 pleomorphism is very common among bacteria. Certain 

 species are more prone to undergo modifications of this 



