SHAPE OF MICROORGANISMS 31 



gummy mass called the capsule. In stained cultures this appears 

 as a halo surrounding the organisms. The presence of a great 

 number of these capsulated organisms in milk gives to it a ropy 

 consistency. The outer coat of the bacteria stick together so we 

 may draw the milk out into long threads. 



Surrounding the true cell is a relatively firm membrane through 

 which the food must pass and which retains the liquid of the cell 

 within bounds. This is the cell wall. Lining the cell wall on the 



.issapj 



# 



Fig. 15. — Bacteria with flagella sur- Fig. i6. — Capsulated bacteria (after 



rounding- body (after McBeth). Buerger). 



inner side is a dense layer of protoplasm, which has a selective 

 action on the food taken up by the cell. If the cell be placed in 

 a strong sugar- or salt-solution the cell shrinks and the ectoplasm 

 is torn from the cell. This is known as plasmolysis. 



Within the center of the cell is a denser material which stains 

 more deeply than the rest of the cell. This is the nucleus and 

 functions in reproduction. It is a debated question as to whether 

 bacteria in the strictest sense possess a nucleus. Scattered through- 

 out the cell may be seen dark granules. These bodies, termed 

 metachromatic granules, may react to stains in such a way as to 

 differentiate them from the rest of the cell and give us informa- 

 tion as to their composition. They are probably the reserve food 

 of the cell. 



