196 /on ma I of Comparative Neurology and Psychology. 



of the central nervous system, but electrical stimulation may drive the 

 central cells beyond the limits of natural activity into morbid processes. 

 From a series of experiments he concludes that activity causes a reduc- 

 tion in size and number of NissL bodies in the cortical cells, and a 

 diffusion of the chromatic substance into the cytoplasm. There is no 

 noticeable change in the nucleolus. This condition is initial to fatigue 

 and becomes more and more accentuated. Finally the cell, making a 

 last effort, comes into a state of fatigue which is accompanied by in- 

 crease in volume of the cell body and disappearance of nearly all the 

 chromatic substance of both the cytoplasm and the nucleus. 



Geeraerd followed these studies with experiments upon recupera- 

 tion. By similar methods he examined the cortex of animals which, 

 after complete exhaustion, had been allowed to rest for periods vary- 

 ing from five minutes to an hour. The first indication of repair was 

 discovered after thirty minutes of rest, when the contour of the cell 

 body is found to have regained its normal condition. After three- 

 quarters of an hour a blue zone appears around the nucleolus, which 

 is finely granular with conical projections reaching out to the nuclear 

 membrane. But while the process of repair seem.s to appear first in 

 the nucleus, the process in the cytoplasm advances from the periphery 

 towards the nucleus. The first tigroid bodies appear next to the cell 

 membrane and gradually invade the deeper regions of the cell. He 

 finds further that while the large pyramidal cells are last to be affected 

 by fatigue they are first to recover. 



Gp:eraerd calls attention to the fact that in the earlier stages of 

 activity the cytoplasm stains a deeper blue than uormal but that this 

 is due, not to an increase in the tigroid substance, but to the breaking 

 up into small granules. He believes that this fact accounts for the 

 erroneous position taken by certain authors that activity causes an in- 

 crease in the tigroid substance. 



In comparing the retina of a bird which had been subjected to a 

 bright light for a prolonged period with the retina of another which 

 had been confined for a like period in a dark room, Carlson ('03) 

 finds there is a ^^ constant diffcirncc in the amovnt and appearance of the 

 'Nissl substance in the cells of the ganglionic and bipolar cell layer. The 

 ganglion cells of the stimulated retinae are poorer in Nissl's substance, 

 the Nissl's granules present are less distinct than in the resting retinae, 

 and the protoplasm of the cell bodies takes a diffuse blue stain." This 

 difference is not eciually marked in all preparations nor in all regions 

 of the same preparation. 



The lesions of the nerve cell accompanying anemia have been 



