Hatal, Spenal Ganglion Cells in the Rat. 19 
This decrease occurs gradually, and after the animal reaches 
its mature condition remains nearly constant. The high per- 
centage of water in the whole nervous system indicates that 
the nerve cells probably contain much water; that is to say, it 
appears from this justifiable to conclude that nerve cells in the 
growing condition contain the larger quantity of water and 
since the cells with the larger quantity of water are most read- 
ily shrunken, the phenomena of shrinkage in the small cells 
does not signify a pathological condition, but shows that the 
cell body is physiologically immature, that is contains the 
higher percentage of water which is necessary for its growth. 
Let us compare the structure of the small celis of the adult 
animal with the cells of a young rat. The difference in cell-size 
in the spinal ganglion appears during uterine life. In a white 
rat weighing 4.52 grams differences in size are already quite 
clear. The large cells attain the diameter of about 25 , and 
the nucleus about 12,. On the other hand, the small cells 
only attain 14, in the diameter of the cell-body and their 
nucleus 8.5 ,. In this stage, the small cells have a compar- 
atively large nucleus and little cytoplasm. The stainable sub- 
stance is diffused through the cytoplasm in this early stage. In 
the white rat of 10.84 grams body-weight, the large cells attain 
35 . inthe mean diameter and the nucleus 16 ,. The small 
cells in this stage measure 14.1 , in the mean diameter of the 
cell-body and 9.7, in the mean diameter of the nucleus. 
In the rat weighing 10.84 grams the outlines of the large cells 
are sharply bounded and the cell-body stains strongly with 
methylene blue. The small cells, however, not only maintain 
nearly same size as at birth but also the cell-body shows the 
same appearance as in the case of the new-born rat. 
In the next stage, namely in the rats of 25.1 grams in the 
body-weight, the large cells develop remarkably, attaining 39 » 
in the mean diameter of the cell-body and 13, in the mean 
diameter of the nucleus. The small cells, on the other hand, 
1 The writer observed in the embryo of Amia calva in which difference 
already takes place when it is 6 mm. long. 
