CENTRAL NERVOUS SYSTEM. 



631 



s.O-OO 



ological variations depended on whether it was possible to demonstrate recov- 

 ery from them. This was accomplished in the following manner. 



Under fixed conditions a cat was stimulated in the usual way and the 

 amount of shrinkage in the nuclei of the spinal 

 ganglion-cells was determined. This was found to 

 be almost 50 per cent. Four other cats were 

 similarly treated and then allowed various periods 

 (six and a half, twelve, seventeen, and twenty-four 

 hours) in which to recover. The results appear in 

 Figure 158 and the table on page 630. 



The effects of stimulation described were found 

 not only in the nerve-cells of cats, but also in those 

 of frogs which had been stimulated in a similar 

 manner. 



Having thus shown that the change was physio- 

 logical in the sense that it was one from which the 

 cells could recover, it remained to be shown that 

 the features of the change were discernible in the 

 living cell, and were not caused secondarily by the 

 actions of the reagents employed in preparing the 

 sections. 



For the study of the living cell, frogs were 

 chosen, and the cells of the sympathetic ganglia 

 examined. In these experiments cells from dif- 

 ferent frogs were prepared under two different 

 microscopes and kept alive in the same way by irri- 

 gation with a nutrient fluid. In one case, however, 

 the cell was stimulated by electricity, while in the 

 other no stimulation was applied. During the time 

 of the experiment the cell which was not stimulated 

 remained unchanged, while the stimulated cell went 

 through the series of changes exhibited in Figure 

 159. 1 



So far as the main features are concerned the 

 shrinkage and crenulation of the nucleus was essen- 

 tially similar to that found in the nuclei of the 

 spinal ganglion cells of cats. These results demon- 

 strated therefore the natural character of those 

 changes in the nerve-cells which had been found 

 after treatment with histological reagents. 



It followed that if these changes were really 

 significant of normal processes they should be found 

 in the nerve-cells of those animals which show 

 well-marked periods of activity, alternating with periods of rest. 

 1 Hodge: Journal of Morphology, 1892, vol. vii. 



FIG. 159. Showing the changes 

 in the form of the nucleus result- 

 ing from the direct electrical 

 stimulation of the living sym- 

 pathatic nerve-cell of a frog. 

 The hour of observation is given 

 within each outline. The experi- 

 ment lasted six hours and forty- 

 nine minutes. A control cell 

 treated during this time in the 

 same manner, except that it 

 was not stimulated, showed no 

 changes (Hodge). 



To deter- 



