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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



mine this, birds and bees were examined, one set of preparations being made 

 from animals which were killed at the beginning of the day, after a night of 

 rest, and the other from those killed at the end of the day, after a period of 

 activity. Similar changes were found in the cells of the spinal ganglia of 

 English sparrows, of the cerebrum of pigeons and cerebellum of swallows, and 

 of the antennary lobes of bees (see Fig. 160). 



..a. 



FIG. 160. Spinal ganglion-cells from English sparrows, to show the daily variation in the appearance 

 of the cells due to normal activity : A, appearance of cells at the end of an active day ; B, appearance of 

 cells in the morning after a night's rest. The cytoplasm is filled with clear lenticular masses which are 

 much more evident in the rested cells than in those fatigued (Hodge). 



A study of these figures shows the cells to be turgid with large round 

 nuclei, at the beginning of the day after a night of rest, and on the other 

 hand that they are vacuolated and shrunken and with altered nuclei at the 

 end of an active period. These observations therefore justify the conclusions 

 drawn from the appearances following direct stimulation. 



Other observers 1 have obtained similar results. The motor cells of the 

 spinal cord and cells of the retina (dogs, Mann) have been added to the list 

 of those showing changes. After a short period of stimulation of the sympa- 

 thetic cells of the rabbit, both Yas and Mann have found a preliminary swell- 

 ing of the cell, and the same has been noted by Mann in the case of retinal 

 cells in the dog. 



The application of these observations to changes in the human nervous 

 system has thus far been made only in a casual way, but enough has been 

 already observed to make certain that the results are applicable. 



It will be noted that the changes described follow variations in the amount 

 of stimulation, the nutrient conditions represented by the surrounding plasma 

 remaining nearly coustant. This latter, however, may undergo alteration, and 

 recent observations show that in various forms of poisoning by inorganic sub- 



1 Vas : Archiv fur mikroskopische Anatomic, 1892 ; Mann : Journal of Anatomy and Physiology, 

 1894. 



