CENTRAL NERVOUS SYSTEM. 195 



alteration, and recent observations show that in various forms of poisoning 

 by inorganic substances or in zymotic diseases the nervous system and espe- 

 cially the cell-bodies are affected early and in a profound manner. 1 



Fatigue in Nerve-fibres. — There is no evidence for fatigue changes in 

 nerve-fibres. For the full discussion of this question the reader is referred 

 to page 96. 



Atrophic Influences. — When a nerve-cell is not kept active by the 

 impulses passing within it, it usually atrophies and may degenerate. The 

 reason for this appears to be that the loss of those changes which accompany 

 the nerve-impulses decrease the vigor of the nutritive processes. 



For the detailed study of metabolic changes within the cell-body the 

 method of Nissl 2 has been of prime importance. This method consists in 

 fixing and hardening the nerve-tissue in 96 per cent, alcohol and staining 

 with hot methylene blue. As a result, the cell-bodies especially, retain the 

 stain, and in the cells there is a "stainable substance" characteristically 

 arranged in small masses. 



For a given animal the arrangement of the " stainable substance" is char- 

 acteristic of the cells from different divisions of the nervous system. In 

 a general way, too, cells occupying homologous positions in the central 

 system of mammals tend to have the substance arranged in a similar manner. 

 But the characteristic picture is modified in any given case by the age of the 

 animal and by the pathological conditions which may have surrounded the 

 cell chosen for study. The changes in the picture may be described as 

 variations in (1) the stainable substance; (2) in the non-stainable fibrillar 

 framework which appears to enclose the former. 



In both of these, variations may be accompanied by gross physical 

 changes, i. e., alterations in the size of the cell-body, the nucleus and its parts, 

 and alterations in the position of the nucleus, which may appear pushed to 

 the periphery of a swollen cell, or even extruded from it. These physical 

 changes are, of course, the effects of the action of the alcohol and other 

 reagents employed on the cells altered from the normal, and while these 

 physical changes serve most admirably to distinguish the normal from the 

 abnormal cells, they do not necessarily represent the condition of the abnormal 

 cells during life, a cell with an extruded nucleus, for example, being a ease 

 in point. These changes may ultimately cause the death of the element. 



The stainable substance is found to be extremely sensitive to variations 

 in the physiological conditions surrounding the cell, and therefore to be most 

 important for the revealing of the effect of all sorts of changed conditions, 

 such as starvation, activity, fatigue, injury to the axone, or injury to the 

 afferent neurones bringing impulses to this particular cell, and, finally, the 

 effects of toxins circulating in the blood. 



^Schaffer: Ungarisches Arehivfur Medicin, 1893; Pandi: Ibid., 1894; Popoff: \'irrhow's 

 Archiv, 1S94; Tsehistowitsch : Petersburger medicinische Wochenschrift, 1895. 



1 The publications of Nissl have not yet been printed in a compact form. The voluminous 

 bibliography of the author is given by Barker : The Nervous System, 1S99, pp. 105, 100. 



