Fixation and Fixatives 75 



Thi s very interesting fixative was developed originally for the fixation 

 o f whole eyes but i t may be used very profitably in any place in which 

 nerve structures are to be examined subsequently. The salts of uranium 

 are widely used in fixatives intended solely for the central nervous system, 

 but this particular formula is also useful for general purposes. Fixation 

 should take place overnight, and then the material should be washed in 

 running water. 



Another very little known but admirable fixative is: 



Note: One part of A is mixed with three parts of B immediately before 

 use. 



This is very nearly as good a general-purpose fixative as the mixture of 

 Gilson and has the advantage over Gilson's that objects fixed in it can be 

 handled with steel instruments before being washed. It is not desirable 

 to leave specimens in it too long (certainly not more than 2 or 3 days), 

 and the fixative should be washed out in 70 per cent alcohol. 



OPERATIONS ACCESSORY TO FIXATION 



Removal of Fixatives. Under each of the formulas given above, it has 

 been indicated in what fluid the specimen should be washed to remove 

 the fixative. This simple washing, however, is not always sufficient in the 

 case of fixatives containing mercuric chloride or picric acid. Mercuric 

 chloride occasionally gives rise to long needlelike crystals in tissues. These 

 may be prevented by soaking the specimen, after it has been washed in 

 running water overnight, in: 



Lugol's Iodine: 



Mix 1 g of potassium iodide with 0.5 g of iodine. Add 2 or 3 ml of water 

 and shake until dissolved. Then dilute to 50 ml. If diluted to 150 ml, this 

 becomes "Gram's iodine." 



Note: Iodine is very soluble in strong solutions of potassium iodide and 

 very insoluble in weak solutions. 



After the pieces have been soaked in this solution overnight, they should 



