24 STUDENTS HISTOLOGY 



It serves very well all the purposes of hardening agents. 

 Using small pieces, leave them in the solution twenty-four hours. 

 After washing, place in eighty per cent, alcohol, and subsequently 

 in strong alcohol. Stain with safranin or haematoxylin . 



CHROMIC ACID FIXING AND HARDENING 



Chromic acid is a very deliquescent 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 grams. 



Water 75 c.c. 



For general use, dilute three parts with six hundred 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 watched carefully; and when, on cutting through a 

 piece, the fluid is found to have stained the blocks completely, 

 taking from two to three, or even four weeks, remove to a large jar 

 of clear water and wash, preferably with running water, for twenty- 

 four hours. The w r ashing having removed the chromic acid, the 

 tissue is further hardened in alcohol. 



Very small pieces of tissue maybe hardened in one or two days. 

 Chromic acid is useful to preserve the nuclear figures. 



ERLICKl'S FLUID 



Bichromate of potassium 25 grams. 



Sulphate of copper 10 " 



Water 1,000 c.c. 



This may be employed in precisely the same manner as the 

 dilute chromic acid solution. 



DECALCIFYING PROCESS 



Six per cent, chromic acid solution 9 parts. 



Nitric acid, C. P 1 part. 



Water 90 parts. 



The earthy salts may be removed from teeth and small pieces of 



