APPENDIX B 



SOME STANDARD REAGENTS AND THEIR USES 

 I. FIXING AND HARDENING AGENTS 



1. Acetic Acid. Acetic acid is more commonly used in mixtures 

 or in diluted form than pure. It is valuable because it tends to 

 produce good optical differentiation and facilitates penetration. 

 When employed alone it causes some tissues to swell and disinte- 

 grate. Inasmuch as most fixing agents give the best results 

 when they have an acid reaction, from 1 to 5 per cent, of acetic 

 acid is generally added to acidify them in case they are not nat- 

 turally acid. Acetic acid is also of great value in mixtures be- 

 cause it counteracts the shrinking action of certain reagents. 

 Ordinary acetic acid is of about 36 per cent, strength; glacial 

 acetic, of about 99.5 per cent, strength. 



A strength of from 0.2 to 1 per cent, is recommended by 

 Flemming for work on cell nuclei. Strong glacial acetic acid is 

 sometimes used for highly contractile animals, such as Coelenter- 

 ata, Mollusca, and Vermes. The animal is rapidly flooded with 

 the acid and remains immersed until it is thoroughly penetrated 

 (6 to 10 minutes). It is then washed in repeated changes of 50 

 or 70 per cent, alcohol and left to harden in 70 to 83 per cent, 

 alcohol. The pure acid, if allowed to act for more than a few 

 minutes, swells and softens the tissues. Acetic acid should not 

 be used when connective tissue or delicate calcareous structures 

 are to be preserved. 



2. Acetic Alcohol. Carnoy recommends each of the following 

 formulae : 



a) Glacial acetic acid 1 part 



Absolute alcohol 3 parts 



6) Glacial acetic acid 1 part 



Absolute alcohol 6 parts 



Chloroform 3 parts 



The chloroform is said to hasten the action of the mixture. 

 Either of these reagents penetrates well and acts rapidly. Almost 



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