ISO- 

 hardened in 1 to 2 weeks. After hardening in Miiller's 

 fluid the tissues need to be well washed in flowing water 

 for several hours. They are then placed into 75 % alcohol 

 for 2 or 3 days, and into 95 % for 4 to 6 days ; they are now 

 ready for cutting. Hans Virchow* recommends that the 

 preparation be transferred from Miiller's fluid into 96% 

 alcohol; the tissues must, however, be kept in the dark. 



This method is especially useful for hardening the 

 central nervous system, and when necessary to harden 

 large masses, entire organs, tumors, etc. It is riot used to 

 advantage when the finer structure of cells is desired. 



Nitric Acid (Benda). 



Benda recommends a 10% solution ; in this the tissues 

 remain from 24 to 48 hours, are then transferred to Miiller's 

 fluid for 1 or 2 weeks, thoroughly washed in flowing water 

 for several hours ; and the hardening completed in graded 

 alcohol. This method gives good results when it is desired 

 to harden an entire eye ; the HNO 3 fixes the tissues, and it 

 can then be placed into Miiller's fluid without collapsing. 



The skin and scalp are also well hardened after this 

 method. 



Picric Acid. 



A saturated aqueous solution is kept on hand. Always 

 filter before using. The tissue needs to be cut into small 

 blocks ; they remain in the fluid for 1 to 3 days, are then 

 rinsed in water, and placed in 80% alcohol, which must be 

 changed as often as it becomes yellow ; as soon as none or 

 very little of the acid is given off, place in 95% alcohol. 

 Peripheral nerves, vessels, elastic cartilage, and fibro-carti- 

 lage are well hardened in this way. Fcetal bones are 

 decalcified. 



Flemming's Solution. 



One of the best of hardening solutions is a mixture of 

 chromic, osmic, and acetic acid in the following propor- 

 tions : 



* Quoted by Rawitz Leitfaden, Histologjischer Untersuch- 

 ungen. 



