46 ie vSs) OSs 
of fibrillae are generally recognized, the coarser fibers or net- 
work at the periphery and the more delicate plexus or net about 
the nucleus. The coarse cytoreticulum figured by Donaggio 
in the dog is uniform throughout the cell. Such a difference in 
appearance as compared with Cajal, Bielchowsky, and Bethe 
preparations is probably due to the peculiarities of the technical 
procedure. 
On general principles it is improbable that any networks 
pervade living protoplasm. ‘The point of view developed through 
the progress of colloid chemistry postulates that protoplasm 
consists of a microscopically homogeneous colloidal ground- 
substance in which are microscopic colloidal aggregates of 
eranulations, fibrillae, and the like. There are various catego- 
ries of these, each of which has its own physical and chemical 
peculiarities. This is not merely speculation. The beautiful 
cytoreticula that may be seen in the protoplasm of many eggs 
after acid fixation, sublimate, etc., have been proved to be 
artefacts by the study of the living protoplasm with modern 
optical equipment, by the micro-dissection studies and vital 
staining methods of Kite and Chambers, by the use of less 
violent fixing agents, and by the convincing centrifuging experi- 
ments of Lillie and others. The control of the technical pro- 
cedure in other tissues by the study of fresh material is of especial 
importance for the study of the nerve cell, for here the difficulties 
of observing the uninjured cell are very great. Bensley (11) 
found the acinar cell of the pancreas in the guinea-pig particu- 
larly favorable for postvital study with and without vital stains. 
After an extensive series of experiments with fixatives con- 
trolled by this means, he found that osmic acid mixtures produced 
less change than any other. This was especially true of his 
modification of the Altmann mixture, which he has termed 
‘A. O. B.’ Nerve cells prepared by this method are particu- 
larly worth study, although it must be remembered that in 
such large elements as are considered in this paper it is possible 
that the acetic acid may often reach the center of the cell before 
the osmic acid and so produce the picture of an acid reticulum. 
From a consideration of these facts relative to other cells, I 
