330 THOMAS J. HELDT 



stances of the tissue, especially the chromatin. The relation of 

 the pink and blue portions to each other, and to the different 

 conditions of the technique, will be considered more in detail 

 under subsequent divisions. 



In these stained, preparations the various kinds of cells may 

 be clearly distinguished. Red and white blood cells and glia 

 cells appear, at temperatures above -2o°C. quite unaffected by 

 the freezing, excepting of course those that have been crushed 

 or otherwise distorted in making the smear. Such crushed forms 

 produce areas of coarser network. At lower temperatures ( —25° 

 to -40°C.) these cells, and the nerve cells as well, show^ a con- 

 siderable variety of changes which will be discussed under the 

 headings following. 



c. Nerve cells of smears frozen at -5° to —10°C. The multi- 

 polar nerve cells of smears frozen at the temperature stated 

 present appearances that vary somewhat depending, in addition 

 to the reduction in temperature, on the thickness of the smear, 

 the rapidity of the freezing, and no doubt also on the surface 

 tension and other intrinsic forces of the different cellular ele- 

 ments. The size of the cell does not appear to play so great a 

 part in these variations as one might expect. The change which 

 is the most marked and characteristic of this temperature inter- 

 val, and, in fact, the first change to become noticeable in the 

 cells, is in the Nissl's bodies which become minutely reticular or 

 vacuolated, thus forming many small blue-staining networks, 

 each network corresponding to a single Nissl's body. These net- 

 works are loosely connected together by finer trabeculae of the 

 same blue-staining substance (fig. 3). The trabeculae appear to 

 be direct extensions of the Nissl's substance which has probably 

 a lower freezing point. By virtue of this property these delicate 

 processes have been squeezed out into the surrounding cytoplasm 

 under the force of the displacement brought about by the enlarg- 

 ing and expanding ice masses. None of the networks extends 

 beyond the walls of the cells. Aside from the Nissl's bodies, the 

 cellular cytoplasm, the nucleolus, and the other nuclear struc- 

 tures show as yet no change, unless the nuclear chromatin, exclu- 

 sive of the nucleolus, may be said to be beginning to suggest 



