STIMULI AND THEIR ACTIONS 



465 



the exertion of the day, they have an indented contour (Fig. 

 241, £). Likewise in the cat, after stimulation for several hours, 

 the nuclei of the ganglion-cells, which previously were vesicular 

 and round, are shrunken and have an irregular contour, while the 

 arrangement of the contents has changed materially (Fig. 240). 

 According to Mann, and also Lugaro, the change of the ganglion- 

 cell during its activity consists essentially in a turgescence of the 

 protoplasm and the nucleus, while during rest a diminution in 

 volume takes place. During work the nucleus becomes poorer in 

 chromatin, and, as Lugaro found, by fatigue the nucleolus can 



Pro. 240.— Ganglion-cells of the cat. A, In the normal condition ; B, after five hours' stimulation. 



(After Hodge.) 



be made completely to disappear. Here belong, also, the fatigue- 

 changes which Heidenhain ('83) observed a long time ago in 

 salivary glands after stimulation, the cell-nuclei of which, in rest, 

 put out pseudopodium-like processes, but after stimulation assume 

 the spherical form (Fig. 242). 



The fatigued muscles recover as soon as the stimulation ceases, 

 and the more rapidly, the less was the degree of fatigue. In 

 recovery the irritability gradually increases; the various pheno- 

 mena of fatigue, which can be seen in the curve of contraction, 

 gradually pass away, and, finally, the muscles are in the same 

 condition as before. 



H H 



