NERVE CELLS OF THE CRAYFISH 41 
For neurofibrillae a modification of the method of Donaggio 
(05) proved very serviceable. It is as follows: 
1. Fixation, 24 hours in Heidenhain’s corrosive sublimate. 
Remove excess of sublimate with iodine solution. 
2. 2 to 3 hours in distilled water. 
3. 48 hours in pyridine, changing pyridine after 24 hours. 
4, 24 hours in distilled water, changed frequently. 
5. 24 hours in aqueous solution ammonium molybdate, plus 1 minim hydro- 
chloric acid to 1 gram of molybdate. Solution should be fresh. (I 
used ammonium picrate in place of molybdate.) 
. 24 hours in distilled water, changed a few times. 
. Dehydrate and imbed. Usual procedure. 
8. Stain thin sections, 4 to 5u, in 0.01 per cent thionin, 
(Istained overnight. Stain is removed rather rapidly in dehydration.) 
For the study of the Nissl substance various additional fixa- 
tives were used. MHeidenhain’s corrosive sublimate solution, 
formol bichromate (Regaud-Cowdry), acetic-osmic-bichromate 
(Bensley) and 2 per cent aqueous osmic acid show distinct Nissl 
bodies with irregular clear spaces between them. Formol 
neutralized with magnesium carbonate or the 6:3:1 mixture 
of Carnoy show bodies, but they are not so clearly defined. 
Whether this is due to a different behavior of the stain or to the 
effect of the fixatives was not determined. 
All material was imbedded in paraffin and cut 3 to 7y in 
thickness. 
LITERATURE 
Relatively little work has been done on the cytology of the 
crayfish nerve cell. Holmgren’s theory of the ‘trophospongium’ 
was based primarily on his observations of Astacus as well as 
Lophius cells. His interpretation of the former I have dis- 
cussed in a paper (Ross, 715) in which I suggested confining the 
term ‘trophospongium’ to the capsular septa which extend into 
the cytoplasm. In the comprehensive paper of 1900 Holmgren 
figured a large nerve cell from Astacus which shows the typical 
intracellular axone, but this condition is not referred to in the 
text. Owsiannikow (’00) reported two types of neurofibrillae in 
Astacus cells, the finer fibers forming a network about the nucleus, 
the coarser fibers being peripherally situated and continuous 
