THE STRUCTURE OF BACTERIA. 5 



pliological elements of the cells are in fact 

 primitive organs. The nucleus seems to be 

 specially concerned in the division and repro- 

 duction of the cell ; the membrane serves 

 partly as a means of protection, but also in- 

 fluences reproduction in so far as it limits the 

 size of the cell and modifies nutrition ; the 

 paraplasm consists of food-material, reserve 

 substances, secretions and the various meta- 

 bolic products ; the vacuoles assist in the diges- 

 tion and distribution of nutrient substances ; 

 while the protoplasm, in a more precise sense, 

 attends to respiration and assimilation. The 

 protoplasm possesses also the property of con- 

 tractility, and, in consequence, has the power 

 of changing its place or moving about. 



Bacteria were regarded by Ehrenberg (1838) 

 as very complicated " infusion-animals," while 

 later they came to be looked upon as quite 

 simple vegetal organisms consisting merely of 

 protoplasm and a membrane. At present we 

 halt midway between the conception of great 

 simplicity in organization and that of great 

 complexity. The bacterial cell consists of 

 finely granular protoplasm, which in the small- 

 est forms is apparently homogeneous, and 

 which, according to Alfred Fischer, behaves 

 toward reagents like plant protoplasm. In 

 the cell-body there are sometimes to be seen 



