CHROMIC ACID FIXING AND HARDENING. 21 



the tissue at least twenty times. Wide mouth, well-stoppered bottles, 

 from one ounce to a pint, or even larger, are best ; and they should 

 be carefully labelled and kept in a cool place with occasional agita- 

 tion. 



Quick Method. A piece of any solid organ, say liver, spleen, pan- 

 creas, kidney, uterus, lymph-node, etc., not larger than one half 

 inch square by one-eighth thick, may be perfectly hardened in twelve 

 hours by immersion in one ounce of ninety five percent, alcohol. No 

 more should be thus prepared than is to be cut within twenty-four 

 hours, on account of the shrinkage which results after the prolonged 

 immersion of solid structures in strong spirit. 



After the tissue has been one hour in the above, it maybe hardened 

 in one or two hours more, if transferred to absolute alcohol. This 

 method is of frequent advantage in pathological histology. 



Ordinary Method. The method quite general here, and intended 

 to prevent shrinkage, is as follows : 



The organs, cut into pieces from one-half to three-fourths of an inch 

 cube, are placed in a mixture of alcohol one part, water two parts 

 (called in this laboratory " Alcohol A") for twelve hours. This re- 

 moves the blood, and prepares the tissue for the next mixture alco- 

 hol one part, water one part, ("Alcohol B ") where it remains twenty- 

 four hours. The pieces are afterward removed to ninety-five per- 

 cent alcohol ("Alcohol C"). The strong alcohol completes the hard- 

 ening, and serves as a preservative until such time as sections may be 

 required. The process is complete in from two to four weeks, and 

 the material will keep without deterioration for three or four years, 

 especially if the spirit be changed occasionally. 



Ordinary anatomical specimens which have been preserved in dilute 

 alcohol are of no value for our purpose. 



CHROMIC ACID FIXING AND HARDENING. 



Chromic acid is a very deliquescant salt, and is best preserved by 

 making a strong solution at once, and then diluting it as may be 

 needed. A stock solution may be made as follows : 



Chromic acid (crystals), . . . . 25 grammes. 

 Water (distilled or rain), . . . .75 cubic cent. M. 



For general use, dilute 20 parts with 600 parts of water, which gives 

 a strength of nearly one-sixth of one per cent. 



The tissue, as soon as secured and properly divided, is placed in the 

 above, remembering the rule regarding quantity. Change in twenty- 

 four hours to fresh solution, and again on the third day. In seven 

 days, or thereabout, change the fluid again. The tissue must now be 



