70 Neurological Technique 



While the solutions of oxalic acid and potassium sulphite are often made 

 up in the same bottle, the mixture will be found to work better if the solutions 

 are made separately and, when needed, mixed in equal quantities. When 

 mixed, the liberation of sulphur dioxide should be evident. 



PROCEDURE. 



1. To fix and harden. — Place the material in about 5 times 

 its volume of Miiller's fluid (A). Brains and spinal cords of the 

 larger animals should be divided into several parts to insure a 

 more rapid penetration of the fixing fluid. On the second and 

 fifth days renew the fluid and put away in a closed vessel, pref- 

 erably in the dark, for one month or more. This time may be 

 reduced to 8-10 days by keeping the vessel in an incubator at a 

 temperature of about 40° C. In the incubator the fluid should 

 be changed daily for 3 or '4 days. 



The method is based upon the action of the bichromate of 

 potassium upon the tissue. After 4 or 5 months in the fluid, the 

 tissue may become over-hardened zxiA will imbed with greater diffi- 

 culty, and its staining properties may be impaired. 



2. Having been subjected to the fluid the required time, take 

 such pieces of the tjssue as are wanted and, to remove the surplus 

 bichromate, wash in several changes of distilled water for 2—12 

 hours. Over-hardened tissue maybe greatly improved by two 

 or three days' washing in distilled water frequently changed. 



3. Transfer from the water to 8- 10 volumes of 70 per cent, 

 alcohol. Here the pieces may remain for several weeks, if desired. 

 Too long in alcohol, however, injures the staining qualities. 



4. From the 70 per cent, alcohol, proceed to dehydrate, imbed 

 in celloidin, mount on block, and section as in X, 3, 4, and 5, 

 p. 64. For ordinary purposes make sections 30/1* thick. 



5. To stain. — In a porcelain dish or test-tube heat some of the 

 freshly made Weigert's haematoxylin (B) till it begins to boil, 

 and then let it cool to about the temperature of the body. The 

 action of the heat serves to complete the "ripening" of the 

 stain. 



While the stain is cooling, replace the 70 per cent, alcohol 

 in which the sections are with 50 per cent, for 5 minutes. 



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