THE CELL 61 



relations which are established between these 

 two elements. Isolated one from the other, 

 neither of them is capable of life by itself." 



The various structures which have thus 

 briefly been passed under review are the main 

 constituents, not only of the unicellular organ- 

 ism, but also of all living cells, whether they be 

 gland, nerve, muscle or bone cells. Each of 

 these specialised cells, however, has its own 

 peculiar powers and duties and its own char- 

 acteristic features. In addition to the struc- 

 tures mentioned, a cell may contain fatty sub- 

 stances, vacuoles or cavities containing fluid 

 and even crystals. 



Having now studied the appearance of the 

 cell as it presents itself to us under the micro- 

 scope it will next be necessary to consider the 

 characteristic activities of which it is the seat, 

 and to inquire in how far these resemble the 

 behaviour of inorganic substances and in what 

 ways they differ from them. 



