Microbial Structures and Staining Reactions 101 



spheres occurring in pairs and in chains, and when they are 

 cultivated in sucrose sokitions, the chains are surrounded by a thick, 

 gelatinous, colorless membrane consisting essentially of dextran. 

 The dextran is removed bv selective chemical action and is purified 

 for use in human transfusions. 



GRANULES 

 Ordinary staining technics commonly employed with bacteria 

 reveal at times deeplv stained bodies called metachromatic granules 

 within the cells. Definite agreement as to the origin and the func- 

 tion of these bodies is still not available. Some workers feel that 

 they are particles of reserve food material. Others call them waste 

 products since the granules in some bacteria do not appear until 

 the twilight of the microbe's life, and granules tend to disappear 

 when active microbial multiplication is encouraged by subculturing 

 in a new medium. Chemical analysis reveals these particles to be 

 fat, carbohydrate, or complex nitrogenous compounds. Pronounced 

 development of granules is a characteristic feature aiding in the 

 identification of the etiological agent in diphtheria {Cori/nebac- 

 terium diphtlieriae). The arrangement of granules at the ends 

 (poles) in the plague organism (Pasteurella pestis) is in contrast 

 to the bands and scattered dots seen in the diphtheria organisms. 

 Sulfur and iron granules may be seen in some of the higher bacteria. 



SPORES 

 When bacteria are gradually subjected to increasingly unfavor- 

 able conditions, including lack of water, depletion of available 

 food, and marked temperature deviations from the optimum, many 

 organisms will die. Certain rod-shaped species classified under the 

 family Bacillaceae are able to develop structures called endospores 

 (spore within a cell), which can withstand relatively undesirable 

 environmental conditions. On the other hand, few cocci or spirals 

 exhibit spores. Bacteria lacking these structures are termed vege- 

 tative CELLS. Bacterial spores might be considered to represent a 

 resting stage similar, perhaps, to the hibernation of some higher 

 animals and the encysted stage present among protozoa. Since 



