FATIGUE. 319 



The solid line in this figure relates to another set of 

 experiments. Under the conditions there employed, 

 five hours' stimulation was found to reduce the volume 

 of the nucleus almost 50 per cent. A series of experi- 

 ments was next made in which the stimulation was 

 carried on for five hours, and then different animals 

 allowed to recover for the number of hours indicated, 

 and the condition of the cells examined at the end 

 of the various intervals, extending up to twenty-four 

 hours. The curve shows that there is a gradual return 



FIG. 74. The dotted line indicates the volume of the nuclei of the 

 spinal ganglion cells of a cat after stimulation for the times 

 indicated. The solid line indicates the volume of the nuclei, 

 first after severe stimulation for five hours, and then in other 

 Cats, similarly stimulated, but subsequently allowed to rest for 

 different periods of time. The actual period of rest is found 

 by subtracting five hours from the time at which the record is 

 made. After twenty-four hours of rest the nucleus is seen to 

 have regained its normal volume. (Hodge.) 



of the nucleus to its initial volume. It was thus 

 indicated that the changes in the cell had not over- 

 passed physiological limits. 



This result led to the study of those animals in which 

 there were well-marked periods of activity and repose, 

 and in which an analogous difference should be found 

 between the cells of an animal killed in the morning, 

 after a night of rest, and one killed in the evening after 



