52 L. S. ROSS 
(99), who also demonstrated the origin of the Nissl substance 
from the chromatin of the nucleus in the neuroblast of the pig. 
Because of its demonstration side by side with the other recog- 
nized elements of the cytoplasm, there is no reason for confusing 
it with other substances, in the vertebrates at least, and probably 
also in the arthropods. In no form has its morphology been 
adequately cleared up, nor can we hope for this until it has been 
studied by means of a vital dye in a living nerve cell in situ. No 
such specific dye has yet been found for the Nissl substance 
or for any other form of chromidial substance. There are 
no means, therefore, of knowing whether any of the granules 
seen in fresh cells are ‘cytochromatin,’ as Heidenhain (’11) 
has termed it. In certain small spinal ganglion cells of verte- 
brates (Cowdry, 714), and in the acinar cells of the pancreas 
(Bensley, ’11) the chromidial substance seems homogeneously 
distributed throughout most of the cytoplasm. The colloidal 
particles seem to be ultramicroscopic in size in these cells. Their 
absence from the axone hillock where mitochondria and ground- 
substance are present between the neurofibrillae is significant 
in this connection, for it shows there is a definite arrangement 
of the chromidial substance in the cytoplasm. Its absence 
from the great axone tract of the large crayfish cells is very 
striking (cf. figs. 10 to 12). It is possible that in this case, as in 
other cells where fixing agents produce definite Nissl bodies, 
the material is present intravitam in the form of ‘granules,’ 
but of this there is no evidence. 
Nissl bodies are figured and-described by many authors as 
they appear in fixed and stained cells, but it is very questionable 
if they exist as bodies in living nerve cells. Mott (?12), Marinesco 
(12), and Cowdry (14) could not find the bodies in postvital 
material. Failure attended by efforts to observe them in the 
living nerve cell of the crayfish. It is only after fixation that 
they become evident. I teased out individual cells from the 
abdominal ganglia in normal (0.75 per cent) salt solution, and 
examined them under low power, 4-mm. objective and no. 4 
ocular, and under a 2-mm. Zeiss apochromatic oil-immersion 
objective and no. 4 ocular. Some of the cells were in their 
