CHAPTER XVII. 



THE CHEMISTRY OF THE LIVER. BILE. CELLS IN 

 GENERAL. 



From the earliest days of physiological chemical investiga- 

 tion the composition of the liver cells and the nature of the 

 processes taking place there have been the subject of many 

 studies. It is well known that the liver has a certain definite 

 work to do in the animal organism and of some of the func- 

 tions we have fairly accurate ideas. Of other functions there 

 is much yet in dispute, but it may be said that a number of 

 synthetic reactions are unquestionably carried out through the 

 activity of cell enzymes there formed. Before taking up the 

 special work of the liver cells something should be said of 

 the composition of animal cells in general. 



COMPOSITION OF CELLS. 



In structure all animal cells agree in consisting of two essen- 

 tial parts, a nucleus and surrounding protoplasm. In young 

 cells these two parts are usually easily recognized, but in the 

 old cells of complex structures they assume various forms, 

 bearing apparently little resemblance to the original type. 

 Cells are in general the center of the various chemical reac- 

 tions taking place in the body. Some of these reactions take 

 place in the fluids outside the cell, but by the aid of ferments 

 of cell origin ; most reactions, however, seem to be carried on 

 within the cell, which may be illustrated by the familiar con- 

 version of sugar into alcohol and carbon dioxide by the yeast 

 cell. The enzyme which does this work may, however, be 

 extracted, as has been already shown. 



Of the chemical nature of nucleus and protoplasm not a 

 great deal is known. It is extremely difficult to isolate orig- 

 inal cells from their modified products or tissues in general, 



302 



