350 E. A. KOCHER 



Rats 



Experiment 4- This and the following experiments differ from the 

 preceding in that here the activity was forced to the point of exhaus- 

 tion. In the previous experiments exercise was voluntary. Two half 

 grown white rats from the same litter served for this experiment. They 

 had previously been kept in a cage and well fed. The fatigue rat was 

 kept running in a revolving wheel for one-half hour, having become 

 tired, he refused to run, and clung to the wall of the wheel. The 

 exercise was then changed from running to swimming. The rat was 

 placed in a tank of lukewarm water, where he kept up constant swim- 

 ming in an attempt to escape. At the end of one hour he was quite 

 exhausted, was taken out, and allowed to rest for an hour. He was 

 then made to swim a half hour again, followed by a half hour of rest. 

 This was continued until the total time of swimming was three hours. 

 He was then killed at the same time as the control. The total brain 

 and portions from the cervical and lumbar cords were removed. The 

 brains were cut sagittally, and placed in 10 per cent formalin; the other 

 portions were fixed in Held's fluid. 



Microscopic examination. In this experiment a large number of sec- 

 tions were cut in series, and a thorough search made for constant 

 differences in staining reaction, amount of chromatic material, size of 

 cells and nuclei, etc. No such constant differences appeared as 

 would go beyond the limits of simple variation. In some slides one 

 might be quite sure of a preponderance of cells of a certain type; for 

 example, showing central chromatolysis ; but on actual counting and 

 comparison, the number of such cells will be balanced by an equal 

 number of the same type in the control. 



Forced activity 



Experiment 5. Dogs. Four young fox terrier dogs of approximately 

 the same size and age were used for this experunent; one served for a 

 control, the other three were subjected to continuous running for 

 periods of one, two and a half, and five hours respectively. They were 

 killed immediately after the exercise, and the nerve tissue from the four 

 animals given identical treatment as to fixation, imbedding, staining, 

 and cutting, the four pieces being mounted side by side in the same 

 block of parafhne, and cut with the same stroke of the microtome 

 knife. In this way the effect of exercise of various grades of intensity 

 could be studied in the cells of the anterior horn of the cord, of the 

 posterior ganglia, and of the cerebellum. 



Microscopic examination. Thorough study of all the sections num- 

 bering over a hundred, most of which were made in series, was made in 

 this experiment. The various types of cells described by Dolley were 

 particularly kept in mind, and an attempt made to correlate them with 

 various grades of fatigue. Dolley (7) describes thirteen different stages 

 of fatigue corresponding to different grades of work and over-work. 



