14 IRVING HARDESTY 



terbalanced by the action of the potassium bichromate and bi- 

 chloride of mercury contained, and both these, in addition to 

 the acetic acid, are slow decalcifiers, as well as fixing agents. 



The mixture employed by Held was here made by adding 40 

 cc. of the commercial (40 per cent) formaldehyde and 50 cc. of 

 glacial acetic to 1000 cc. of a 3.5 per cent aqueous solution of 

 potassium bichromate. This mixture, is at first the color of 

 the bichromate solution, but by warming or after standing a 

 few hours it turns a greenish brown as the result of oxidation 

 processes. It is recommended as best applied after this change 

 })egins. While the reaction between the formaldehyde and po- 

 tassium bichromate must set free some formic acid, and while 

 formic acid, acetic acid and even formaldehyde to a less extent, 

 acting alone, cause the tissues to take up water and thus pro- 

 duce swelling, the mixture with the excess of bichromate seems 

 to produce no swelling of the tectorial membrane nor of the ele- 

 ments of the organ of Corti. 



An advantage of both this fluid and Zenker's is that speci- 

 mens may remain in them for a long period without injury, 

 and it is necessary for the cochleae to remain subjected till the 

 desired decalcification has occurred. Here, the cochleae, brought 

 from the slaughter-house in vials of fixing fluid, were suspended 

 in large amounts of the fluid contained in low cylinder jars with 

 cap covers. The jar, holding about one liter, was filled two- 

 thirds full of the fluid and the cochleae suspended in it near the 

 surface that they might be surrounded by fluid more free from 

 the salts resulting from the decalcification, which salts sink to 

 the bottom. Also they were suspended that they might be 

 subjected to less pressure than if lying on the bottom. The 

 string by which a cochlea was suspended hung over the edge and 

 outside the jar, held in place by the cover, and to the outer end 

 of the string was attached a label when necessary. Adult cochleae 

 required three to four weeks for complete decalcification, the 

 fluid being renewed twice a week. Decalcification sufficient 

 for microtome sections can be judged by testing with a needle, 

 being careful to pierce the specimen in the region of the vesti- 

 bule. The thinner walls of the bony labyrinth of the cochlea 



