93 



This is quite similar to Miiller's fluid in its action, and may be employed in the 

 same cases. It is generally used for the central nervous system. 



Harden in an abundance of the solution for 2-8 weeks, beginning with the 

 2% solution for 2-6 days, 3% solutiort 1-3 weeks, 5% solution 1-3 weeks. 

 Wash out in running water 24-48 hours. Place in 67^)^ and S2% alcohols sev- 

 eral days, keeping in the dark meanwhile, changing when the alcohol is 

 colored. 



^ 32. Chrome-oxalic (Graf). Formula: 8% aqueous solution of oxalic 

 acid, 4 parts ; 95% alcohol, 3 parts ; \% chromic acid, 3 parts. Mix the solu- 

 tions in the order given. 



Fix tissue in the solution 1-6 hours, wash in running water ^-i hour, and 

 harden in 50%, 67%, and 82^ alcohols. 



This appears to be a good general fixer for many organs ; it penetrates 

 well, the tissue cuts well after this method of fixation, and the staining is sharp 

 and strong. 



\ 33. Alcohol. 95%, 67-70%, absolute alcohol. The employment 



of most of the fixers so far mentioned requires the expenditure of considerable 

 time, rendering them inapplicable or unsuitable in many instances. 95% alco- 

 hol itself answers admirably for most histologic objects, fixing well, hardening 

 and likewise dehydrating ( | 4 1 ) preparatory to imbedding in paraffin or col- 

 lodion, affording thus a considerable economy of time. It is also most service- 

 able in pathological tissues where the presence of bacteria is suspected. In 

 some instances 67% alcohol answers as well or better, while in other cases ab- 

 solute (99%) alcohol should be employed. The addition of 5% glacial acetic 

 acid increases the penetrating power and improves the cutting quality of objects 

 containing much connective tissue. 



Fix in 95% alcohol for 1-3 days, changing two or three times, after 3 or 4 

 and after 24 hours. The tissue will probably be found to be dehydrated and 

 ready for the next step of the imbedding process (^ 44 or 52). Stain as you 

 wish. 



\ 34. Formaldehyde. Solutions of this chemical have been found to be 

 goiod preservatives and hardeners and fairly good fixers. It penetrates rapidly, 

 and preserves the natural transparency and pigmentation of the tissue, making 

 it valuable for gross anatomy and museum purposes. As a fixer, an aqueous 

 solution of 2-4% strength may be employed, or it may be used in conjunc- 

 tion with other chemicals, as picric acid, in picro-formalin, or chromic acid and 

 acetic acid. 



Fix 12-24 hours, remove to 67% alcohol for a day, 82% alcohol one to 

 several days. Stain as you wish. 



? 35. Perenyi's fluid. Formula: 10% aq. sol. nitric acid, 4 parts; 95% 

 alcohol, 3 parts ; %% aq. sol. chromic acid, 3 fparts. An embryological fixer 

 of much value. It is also serviceable for general work. 



Fix tissue for 4-5 hours, place in 67% alcohol for 24 hours, 82% alcohol 

 several days. 



I 36. Picro-nitric. Formula: Water, 95 c.c. ; nitric acid, 5 c.c. ; picric 



