ORGANIC CHEMISTRY AND CELL DIVISION 95 



seen, it is possible that alveolar substance and interalveolar substance 

 may differ about as much or as slightly as a colloid and an emulsion. 



The early workers on the cell saw very thin fibers in the proto- 

 plasm, and established the "filar" or "reticular" theories of protoplasmic 

 structure. We now know that if the alveoli are arranged in rows the 

 liquid between the alveoli will appear like threads, although we have 

 not been able to find that these so-called fibers have any important func- 

 tion. These theories, therefore, are not among the important biological 

 problems now. 



When cells are prepared and stained for study in the laboratory 

 they have many granules distributed within them. These may be coag- 

 ulation products of the interalveolar protoplasm, or the cut ends of 

 fibers or cell inclusions of various kinds. 



The great mass of protoplasm is really an emulsion. The tiny bub- 

 ble-like particles or alveoli and the liquid in which these float are called 

 by the physical chemist "phases" of a "system." It can, therefore, be 

 understood that the various surface phenomena which interest the 

 physical chemist are to be found in the living cell, and any chemical 

 knowledge of this nature which the student of the cell can obtain will 

 stand him in good stead. Much of the activity of protoplasm can be 

 explained by a study of surface tension. 



It is to be borne in mind that protoplasm is never solid, although 

 solid particles may and most often are included within its liquid or semi- 

 liquid mass. 



Protoplasm is made up of both organic and inorganic substances. 

 Organic. 



A. Always present. 

 Enzymes. 

 Non-enzymes 



Carbohydrates, 

 Lipoids, 

 Extractors, 



Intermediate products of metabolism. 

 B. Not always present. 

 Pigments, 

 Hormones, 



Aromatic compounds, 

 Toxic compounds. 



The enzymes are continually attempting to produce an equilibrium 

 in the cells. They are chiefly protein in nature and speed up the chem- 

 ical reaction. They may be killed by light or heat. Their activities 

 are specific, each type of enzyme doing only one particular type of work. 

 Every step in the breaking down of proteids is done by a specific 

 enzyme. 



