GANGLIA. I0 g 



GANGLIA. The ganglia are enlargements, usually macroscopic, oc- 

 curring in the course of the peripheral or sympathetic nerves. They always 

 consist of nerve fibers between which there are rows or rounded groups 

 of the bodies of nerve cells. Nerve cell bodies vary in diameter from 

 4 to 150 ft. Thus they include some of the largest cells in the body. Each 

 has a single round or oval nucleus which appears vesicular because of its 

 small amount of chromatin. It contains usually one large round nucleolus. 

 These nuclei are so characteristic that the student should soon learn to 

 recognize them. Near the nucleus the centrosome has been detected, 

 sometimes represented by a number of granules; but mature nerve cells 

 never divide and if destroyed they cannot be replaced. In ordinary 



Blood vessel. 



Fat. 



Ganglion cells. 



Nerve fibers. 



Perineurium. 



root 

 of a spinal nerve. 



Center 



of the 



spinal 



ganglion. 



FIG. 133. LONGITUDINAL SECTION THROUGH A SPINAL GANGLION OF A CAT. X 18. 



specimens the protoplasm is densely granular. There is no cell membrane. 

 Except in the embryo, nerve cells all have one or more processes; and 

 according to the number of these, one, two, or several, they are designated 

 unipolar, bipolar, and multipolar respectively. The processes cannot be 

 traced in ordinary specimens because of their thick entanglement with 

 those of other cells. In studying them the special methylene blue and 

 silver (Golgi) methods are employed. If pieces of very fresh nerve tissue 

 are placed in a dilute soution of methylene blue, after an hour or more 

 the processes of certain cells are stained so that they can be followed satis- 

 factorily. By Golgi's silver method a black precipitate occurs in and on 



