140 Journal of Comparative Neurology. 



Like this writer, I also found that twenty-four hours in the 

 formol-bichromate is sufficient for hardening and that tissues 

 may then be transferred to pure bichromate. He employed a 

 2)%% solution, however, while I, since it seemed to act more 

 quickly, used a 5% solution. 



From three to four or five days immersion in formol-bi- 

 chromate are necessary for obtaining impregnations of nerve 

 fibers, and almost three for the cells, while the tracheae may 

 be incrusted almost to the exclusion of nerve fibers after one 

 or two days. 



The more or less inevitable precipitate and crystals were of 

 course met with, but on the whole my preparations were com- 

 paratively free from them. In tact, judging from the printed 

 experiences of others, I seem to have been more favored than 

 is usual. Only a few cases occurred out of the hundreds of 

 brains sectioned where the precipitate at all resembled the fine 

 branching of the nerve fibers, and in these there was no ground for 

 a deception of the practiced eye, for the angular contours of the 

 precipitate readily distinguished it from the rounded ones of the 

 fibers. 



The precipitate gave the greatest annoyance in the layer of 

 cell-bodies. This is so thin on the more exposed parts of the 

 brain that it was usually completely obscured when the brains 

 were brought into direct contact with the fluids. Attempts were 

 made to obviate this difficulty. Formic acid was tried and dis- 

 carded, as was also Berkeley's (95) suggestion of adding a few 

 drops of phosphomolybdic acid to the silver solution just before 

 using. The latter can, in fact, do nothing more than weaken 

 the solution of silver nitrate, and one may therefore as well take 

 a weaker solution to begin with. When this is done and the 

 tissue, after first quickly washing off the bichromate with water, 

 is carefully rinsed in the weak solution, or one that has been 

 previously used, before it is allowed to stand, one will be much 

 less troubled with the incrustation. 



This method did not prove as good, however, as one in 

 which the brain was left i7i situ in the head, enough only of the 

 front, top, or side of which was cut away to allow the fluids to 



