26 THE MICROSCOPIC PREPARATION. 



tion. 2 c.c. of glacial acetic acid may also be added. Tissues fixed by 

 either of these fluids may be treated with pyroligneous acid or tannin. 

 The crystals of sublimate must be removed by iodized alcohol. 



Nitric Acid. Small objects may be fixed in about six hours in 

 3% to 5% nitric acid (sp. gr. 1.4). A longer immersion is injurious, 

 as certain nuclear structures are affected. After washing thoroughly in 

 running water, the tissues are treated as usual with alcohols of increasing 

 concentration. 



Chromic acid is used in a "fee-fa to i% aqueous solution. 

 Small pieces are fixed for twenty-four hours, larger ones for a longer time, 

 even weeks. The quantity of the fixing fluid should be at least more 

 than fifty times the volume of the tissues to be fixed. The objects are 

 subsequently washed in running water and run through the ascending 

 alcohols. This last should be done in the dark. 



Two or 3 drops of formic acid may be advantageously added to 

 each 100 c.c. of chromic acid solution (C. Rabl). 



Miiller's Fluid. 



Potassium bichromate 2 to 2.5 gm. 



Sodium sulphate I " 



Water loo c.c. 



With this solution it requires several weeks for proper fixation, and the 

 process must be conducted in the dark. During the first few weeks the 

 solution should be changed every few days, and later once a week. 

 According to the results desired, the pieces are either washed out in run- 

 ning water and subsequently treated in the usual manner with alcohol, or 

 they are placed directly in 70%, which is later replaced by 80 % and 

 90% alcohol. It is important that all these procedures should take place 

 in the dark. 



The use of Erlicki's fluid (potassium bichromate, 2^ gm.; cupric 

 sulphate, 0.5 gm., and water, 100 c.c.) is quite similar to that of 

 Miiller's, except that it acts much more quickly. A temperature of 30 

 C. to 40 C. shortens the process in both cases considerably, Miiller's 

 fluid fixing in eight and Erlicki's in three days. 



Tellyesnicky's Fluid. This solution gives better nuclear fixation 

 than Muller's fluid. 



Potassium bichromate 3 S m - 



Glacial acetic acid 5 c - c - 



Water 100 " 



Small pieces of tissue remain in this fluid for one or two days. 

 Larger pieces may also be used, but require a longer period of fixation. 

 Wash thoroughly in flowing water. Dehydrate in graded alcohol, 

 beginning with 15%. 



Zenker's Fluid. 



Potassium bichromate 2.5 gm. 



Sodium sulphate I " 



Corrosive sublimate 5 " 



Glacial acetic acid 5 c.c. 



Water 100 " 



It is advisable to add the glacial acetic acid in proper proportion to 

 the quantity of the solution to be used, and not to add it to the stock solution. 

 The tissues are allowed to remain for from six to twenty-four hours in this 



