Content of the Cell 29 



granules of sulfur which they later burn up for the sake 

 of the energy that can be thus derived. 



The protoplasm also contains various amounts of 

 organic and inorganic salts in solution, derived from the 

 surrounding medium, and compounds formed from these 

 by the bacterial protoplasm. 



The absorption of food.— The substances dissolved 

 in the culture medium pass, without difficulty, through 

 the cell-wall, and the latter is, therefore, said to be 

 permeable to the dissolved substances. On the other 

 hand, the protoplasm is penetrated to only a slight ex- 

 tent, and is, therefore, said to be impermeable. These 

 physical properties are of vital significance, not only 

 in the nutrition of the organisms, but also in their 

 resistance to the entrance of injurious substances. 



