THE UNIT OF BIOLOGICAL ACTIVITY 151 



THE MECHANISM OF CELLS 



In the early stages of this book Guilliermond has revealed the struc- 

 tures of microbial cells and has indicated in his treatment the probable 

 relations of these structures to functioning. The immediately fore- 

 going section carries the suggested creative powers of the various cell- 

 structures to molecular foci which seem to be the centers in which vital 

 changes are occurring. It now remains to set forth the mechanism of 

 the cell, functioning as a whole, which can be done only by approaching 

 it through the channels of its activities. 



A living organism is conspicuous as a mechanism because it has the 

 power of self-maintenance in the presence of a suitable environment, 

 it can reproduce its like when conditions are favorable, it frequently has 

 the freedom of motion, and possesses many reacting responses to stimuli 

 or expressions of dynamic existence. These are characteristics which 

 belong peculiarly to cell-life. 



With food at hand and other favorable conditions the cell becomes 

 an automaton. The material needed in growth and the energy required 

 for operation are obtained without assistance and regulated to meet the 

 exact demands of the cell. If food is plentiful, growth and reproduction 

 reach out to conserve it; if food is scarce, the cell accommodates itself to 

 its limitations by reduced activity or a resting stage. This great power 

 of adjustability while having boundaries, is as useful to the life of the 

 cell as it is wonderful. Likewise, if solid food alone is available, the 

 food is reduced to a liquid form or changed that it may be incorporated 

 in this bit of protoplasm, the cell. When there, it is transmuted into 

 the living substance or is converted from dead matter to living matter. 

 In performing this work, the food consumed has had to provide the 

 energy as well as the material which rejuvenates the protoplasm, for 

 this constant rejuvenating process in the case of protoplasm seems 

 essential to life as well as to the constant supply of energy to make it 

 possible. 



There are agents, or properties, or substances of the cell which make 

 this possible, it is true, and there are structures of the cell which are 

 involved in it, but these are necessarily subordinate to the innate proto- 

 plasmic forces which give them birth and which in some manner create 

 and supervise them. These detailed features are the subjects of physi- 

 ological study. 



