798 



THE NERVOUS SYSTEM. 



by Nissl. ' Subjected to this technique nerve cells present two very different types ol 

 reaction. Certain cells, such, for example, as the cells of the granule layers of the cere- 

 bellum and of the olfactory lobe, stain only as to their nuclei, the cell bodies themselves 

 remaining entirely unstained. To such cells Nissl has given the name of caryochromes. 

 It is obvious that the method of Nissl gives no insight into the structure of these cells. 

 The majority of nerve cells, however, react both 

 as to their nuclei and as to their cell bodies to 

 the Nissl stain. These cells Nissl designates as 

 somatochromes. Such a cell presents the follow- 

 ing appearance (Plate XIII., 1). There is a nu- 

 cleus identical in structure with nuclei found in 

 other cells. It is bounded by a nuclear mem- 

 brane and traversed by a network which takes a 

 comparatively light blue stain. Within the nu- 

 cleus is a nucleolus staining an intense blue. 

 In the cell body two distinct elements appear: 

 a clear ground substance, unstained; and scat- 

 tered through it deep blue staining masses, 

 known as chromophilic bodies. These chromo- 

 philic bodies are granular, and differ in size, 

 shape, and arrangement. These differences 

 have served as a basis cf classification. Pre- 

 senting variations in different types of cells, 

 their appearance in a given type remains con- 

 stant. Most investigators, while differing in 

 details, agree in ascribing to the unstainable 

 substance a definite structure. This structure 

 is usually described as composed of a fibrillar or 

 reticular network lying in a more or less homo- 

 geneous ground substance. With the use of the 

 ordinary technique of Nissl, all of the cell body, 

 excepting the chromophilic bodies, remains un- 

 stained and apparently structureless. Our ideas 

 as to the physiology of these different elements 

 of the nerve cell rest largely upon a theoretical 

 basis. It has been shown that the nerve cell 

 represents the genetic centre of the neurone. 

 From the behavior of the processes, when cut 

 off from the nerve cell, it is evident that the cell 

 body represents the nutritive or trophic centre 

 of the neurone. It seems probable that from the 

 standpoint of neurone activity, the cell body re- 

 presents the functional centre of the neurone, 

 while the processes act as organs of reception or 

 of distribution. Certain facts, such as the entire 

 absence of the chromatic substance in many 

 nerve cells, in the axones of all nerve cells, and 

 its diminution during functional activity and in 

 fatigue, together with its behavior under certain 



pathological conditions, lend weight to the view that the stainable substance of Nissl 

 represents a food element of the cell. The achromatic element, on the other hand, is 

 continuous with the fibrillae of the axone, and is considered by most investigators as repre- 

 senting the essential nervous mechanism of the cell. The relation of the Nissl picture 

 to the conditions existing in the protoplasm of the living cell still remains an unsolved 

 problem. The importance of the Nissl method from the standpoint of pathology lies 

 in the fact that when subjected to a given technique, a given type of nerve cell presents 

 1 See Nissl 's method of staining, p. 838. 



FIG. 523. NEURONE (NERVE CELL OR 

 GANGLION CELL AND PROCESSESJ FROM 

 HUMAN CEREBRAL CORTEX. 



Showing main or apical dendrite passing 

 upward and numerous smaller dendrites 

 coming off from the main dendrite and from 

 the body of the cell. A single axone (axis- 

 cylinder process) passes downward from the 

 base of the cell, giving off two collaterals. 



