10 A TEXTBOOK OF PHYSIOLOGY 



an active acid radicle e.g., potassium chroma' e or one with an 

 active basic radicle e.g., rosanilin acetate. The granules with 

 affinity for acid radicles are basic, those for basic are acidic in nature: 

 still other granules are neutral and stain with both radicles: the 

 names given for these are respectively oxyphil, basophil, and 

 neutrophil granules. The first and last are most common. A 

 constant element of the cell is the nucleus. It consists of nuclear 

 plasma and nuclear network. The form of the nucleus varies, but 

 corresponds in general to the shape of the cell large and round in 

 nerve cells, long and oval in involuntary muscle fibres, irregular neck- 

 lace-shaped in leucocytes. Especially large nuclei are found in young 

 ova and nerve cells. The nuclear reticulum consists of granules of 

 nuclein, which stain deeply with basic dyes, and is thus called chro- 

 matin by histo'ogists. The basic affinity of nuclein is due to the 



FIG. 7. - YEAST CELLS PHOTOGRAPHED BY ULTRAVIOLET LIGHT THROUGH QUARTZ 



LENSES. (Barnard.) 



nucleic acid it contains. This substance is rich in phosphorus, as 

 may be shown by special staining methods. The nuclein granules are 

 embedded in a less stainable network the linin. Embedded in the 

 nucleoplasm are one or two larger granules which do not behave to 

 chemical reagents in the same way as the nuclein ; these are called 

 nucleoli. Surrounding the resting nucleus is a perforated nuclear 

 membrane, through which cell protoplasm and nucleoplasm are in 

 continuity. 



The nucleus seems to be the mainspring of the cell's activity. 

 Wherever in a cell growth is active, there seemingly is placed the 

 nucleus (Fig. 8). It controls the cell metabolism and its reproduction. 



In the case of the protozoa, when the nucleus is separated off with 

 one part of the cell, that part grows; the remainder ceases to grow, and 

 dies. 



