FIXATION 725 



tially avoided by the addition of a little iodin to the stronger alcohol, 

 or by combination with acetic acid, thus: 



Glacial acetic acid 5 c.c. 



95 per cent, alcohol 60 c.c. 



Distilled water 35 c.c. 



After fixation for three to twenty-four hours the tissues are washed, 

 and hardened by immersion for twenty-four hours in each strength of 

 graded alcohol (50, 70, 80 and 95 per cent.), and may be kept indefinitely 

 in 80 per cent, alcohol. Tissues should always be stored in 80 per cent, 

 alcohol. Lower grades tend to macerate, higher grades to harden unduly. 



Carnoy recommends also a mixture of glacial acetic acid and abso- 

 lute alcohol in the proportion of 1 to 3 ; this gives excellent results with 

 muscular tissues. 



Tissues for fixation by these or any subsequent method are pref- 

 erably cut into small cubes; a size not exceeding 0.5 to 1 cm. is most 

 desirable. If larger pieces of tissue are necessarily used, the reagents 

 will each require increased time to insure complete penetration. 



Mercuric Chlorid (Corrosive Sublimate). This salt is to be used in 

 saturated aqueous solution. As it dissolves with difficulty in cold water, 

 the use of a hot, normal saline solution hastens the operation. 



Mercuric chlorid is an excellent fixative for cytoplasm, but gives still 

 better results when combined with a nuclear fixative such as acetic acid. 

 The following is an excellent method for general use: 



Mercuric chlorid 7 grm. 



Sodium chlorid 0.75 grm. 



Distilled water 95.0 c.c. 



Just prior to use add 5 c.c. of acetic acid. 



Small pieces of tissue remain in this corrosive acetic mixture for 

 two to twenty-four hours, and are then transferred to graded alcohol, 

 beginning with 70 per cent, and remaining twenty-four hours in each 

 strength. Most dyes will act perfectly on tissue fixed in this way. If, 

 however, the presence of mercury interferes with the action of a dye, 

 this salt can be readily removed by the addition of a few crystals of 

 iodin to the higher grades of the graded alcohols, renewing the iodin if 

 necessary until it is no longer decolorized. 



Formalin. Tissues may be fixed in formalin (formol), a 40 per 



