26 



MICROBIOLOGY 



Granules. In the place of spores there very often 

 appear in the bodies of certain species of bacteria, especially 

 the rod-shaped forms, minute, or larger, more or less irregu- 

 lar granules. In the unstained organism they are light re- 

 fracting. In stained preparations they appear as deeply 

 stained irregular masses, known as metachromatic granules. 

 They have a strong affinity for dyes, thereby staning more 

 rapidly and deeply than the rest of the organism and they 

 are decolorized with great difficulty. In certain bacteria, 

 such as that of diphtheria, they are practically constant, 

 which gives them much value in diagnosis. Besides these, 

 there are often present other concentrated masses of proto- 

 plasm. In stained preparations of bacteria there appear 

 very frequently small irregular areas which do not take the- 

 stain and which are referred to as vacuoles. 



Plasmolysis. When living bacteria are placed in a 

 solution containing an osmotic substance, such as in a 2.5% 



solution of saltpeter or a 1% solu- 

 tion of salt, the osmotic pressure 

 of the outside solution overcomes 

 the normal pressure of the bac- 

 terial contents. Under such con- 

 ditions a current is established in- 

 to the body of the bacterium. The 

 protoplasm of the organism as a 

 result retracts from the cell wall. 

 This is shown by the dense mass- 

 es of protoplasm arranged at the 

 poles or irregularly placed within 

 the bacteria. The clear areas 

 appear as vacuoles. 



Fig. 10. Plasmol3*sis. 

 Figures showing different 

 forms of condensed body 

 contents. 



Reproduction in lower bacteria. The lower bacteria 

 reproduce by cell division or fission. Bacteria multiply under- 

 favorable life conditions only. The young organisms elon- 

 gate until they reach the size of the adult when over the- 

 center of the long axis thus formed there will appear a slight 



