APPENDIX. 391 



Moderate sized pieces of tissue remain in the solution 18-24 hours; then 

 ere washed in running water 3-5 hours ; and carried through 50, 70 and 95 

 alcohol, each for one day. This fluid is excellent for large embryos. 



Mullet's Fluid. 



Potassium bichromate 25-30 gm. 



Sodium sulphate 10 gm. 



Water 1000 cc. 



This classic fixing fluid requires prolonged action, from two to eight 

 weeks or longer, and a large excess in proportion to the volume of the ma- 

 terial. During the first week, the fluid should be changed daily, or in the be- 

 ginning oftener if it becomes turbid ; thereafter, each week. After a variable 

 time, the tissue is washed in running water for 1 224 hours and then trans- 

 ferred to 70 alcohol and placed in the dark, with occasional renewal of the 

 spirit. If, however, the material be nervous tissue intended for subsequent 

 "treatment with special methods, such as Weigert staining, it is transferred, 

 after slight rinsing, directly to the alcohol. This classic fluid, although 

 hardening evenly and without shrinkage large masses, as entire small brains 

 and cords, has the disadvantage of being not only tedious but also lacking 

 in accurate nuclear fixation. Since> however, it is the basis of several com- 

 binations of value, its preparation as a stock solution is desirable. 



Orth's Fluid. 



Miiller's fluid 100 cc. 



Formalin (40 p.c. solution) 10 cc. 



The two solutions are mixed just before using and the tissue, cut into 

 pieces i cm. or less in thickness, allowed to remain not over four days, with 

 two changes. Thorough washing in running water for 18-24 hours is im- 

 portant, followed by 80 alcohol. This fluid yields excellent results, the cel- 

 lular fixation being satisfactory and the required time not excessive. Small 

 pieces of tissue, not exceeding .5 cm. in thickness, may be fixed and hard- 

 ened within a few hours if kept at a temperature of 45 C. in an oven. 



Formalin Solution. 



Formalin (40 p.c. solution) 10 cc. 



Water 90 cc. 



Objects remain for 48 hours, or longer, and are then transferred to 95 

 alcohol for at least two days. This 4 per cent, aqueous solution of formal- 

 dehyde has convenience as its chief recommendation, since, when used alone, 

 it is deficient as an accurate fixative and often does not favor staining. 

 Where, however, the gross features of a specimen are to be supplemented 

 by microscopic examination, formalin offers a satisfactory compromise for the 

 anatomist or pathologist and the histologist. Another important use of this 

 formalin solution should be remembered, namely, the preservation of em- 

 bryos. The reagent is so readily obtained, that the gynecologist, upon whom 

 the embryologist must depend for his supply of human material, can secure, 

 with little trouble, valuable specimens which are too often lost. 



Flemming's Solution. 



Osmic acid (2 p.c. aqueous solution) 4 parts. 



Chromic acid ( i p.c. aqueous solution) 15 ' 



Glacial acetic acid . i " 



