4 NORMAL HISTOLOGY. 



many of these fluids, precipitates certain of their 

 albuminoid constituents, thus diminishing their tran- 

 sparency. It is in general to be used at first in a 

 dilute form, 60 per cent. After 24 hours this is re- 

 placed by 80 per cent., and after another 24 hours by 

 strong 90 per cent. The tissue to be preserved in 

 alcohol, as in other hardening agents, should be small, 

 I or 2 cms. on a side, and the quantity of fluid should 

 be abundant, as much as a hundred-fold. Certain 

 structures are best preserved by plunging them at 

 once into strong alcohol. 



CJiromic Acid is used in aqueous solutions, the 

 strength varying from one sixth to one half per 

 cent. It is very slow in its action, requiring weeks 

 to accomplish its purpose. The fluid should be re- 

 newed at the end of the first, third, and fifth day. 

 After completion of the hardening, the specimen is 

 washed well in water, and preserved in alcohol. 

 After allowing the specimen to remain in the 

 chromic-acid fluid for two weeks, the hardening 

 may be completed in alcohol, after washing well in 

 water. A prolonged action of chromic acid renders 

 specimens brittle. 



Flemming's Mixtures. These give excellent re- 

 sults, especially for nuclear structures. The bits 

 of tissue should be very small, and the best results 

 are obtained when the fluids are allowed to act for a 

 short time twelve to sixteen hours. At the end of 

 this time they are well washed in water and then 



