90 GEORGE W. BARTELMEZ 
oil or bergamot oil and embedded in paraffin. The dehydration, 
clearing and embedding should not occupy more than 6 hours. 
The sections are cut from 6 » to 10 u» thick and are best cleared 
in benzole. Entire heads of larvae prepared in this way showed . 
some cells in every nucleus stained with all their processes, in- 
cluding the axone, and in many of them the endings of the fibers 
of the VIII nerve in the internal ear were perfect. The thin 
sections necessitate the cutting of many series in planes dictated 
by the direction of the fibers to be studied. 
Some of the clearest pictures of the synapses of Mauthner’s 
cell were obtained by a procedure that has not been used before 
on this material (figs. 11-13). Brains were fixed in the mixture 
recommended by Maximow (’09): 
Zenker’s stock solution (without acetic acid) 8 parts 
40 per cent formaldehyde solution neutralized with MgCO; 1 part 
2 per cent aqueous solution of osmic acid 1 part. 
Fix for 6 to 18 hours, renewing the solution after the first 3 
_ hours. Cut in paraffin 4» to 8 » thick and stain with iron hema- 
toxylin. ‘By this means the cells and their most delicate proc- 
esses are preserved with a minimum of shrinkage. In addition 
the myelin sheaths are blackened, and thus a series of larval 
brains of different ages gives an account of the order of myelina- 
_ tion of the fiber tracts, an invaluable aid in the analysis of the 
tracts in so complicated a region of the brain as the anterior end 
of the oblongata. 
It is a pleasure to acknowledge my indebtedness to Professor 
Herrick for his help and: advice and to the other members of 
this department for their coéperation. The larval trout mate- 
rial was obtained through the courtesy of Dr. Raymond C. Os- 
burn at the New York Aquarium and worked up in the labora- 
tory of Prof. C. L. Bristol of New York University. I wish to 
thank both gentlemen for their help. 
