Appendix B: Some Standard Reagents and Their Uses 167 



This mixture is recommended in some cases for the treatment 

 of embryos, especially when the nervous system is to be studied. 

 It penetrates well and preserves faithfully; the alcohol counter- 

 acts the swelling effects of the acetic acid and the formalin. 

 Material may remain in it without injury for several days. The 

 fluid should sooner or later be replaced by 70 per cent, alcohol. 

 No preliminary washing is necessary. 



19. Formol Sublimate (Worcester's fluid). a) Make a satu- 

 rated solution of corrosive sublimate in 10 per cent, formalin. 

 This reagent is recommended by Raymond Pearl (Journal of 

 Applied Microscopy, Vol. VI, p. 2451) as "extremely satisfactory" 

 for killing and fixing protozoa. Washing may be done in water 

 or 4 per cent, formalin. The material may be preserved in 4 per 

 cent, formalin or carried up the grades of alcohol to 70 per cent, 

 alcohol. 



6) If to 9 parts of this formol-sublimate mixture, 1 part of 

 glacial acetic acid is added, Worcester's formol-sublimate-acetic 

 mixture is obtained. Pearl recommends this highly for teleost 

 eggs and for embryological material in general. It will not pro- 

 duce coagulations and cloudiness in the gelatinous envelopes of 

 amphibian eggs, if thoroughly washed out after fixing. Preser- 

 vation is the same as for a). Johnson (Journal of Applied Micro- 

 scopy, Vol. VI, p. 2652) also recommends this reagent very 

 highly for general work except in the case of nervous tissue. 



Personally, I have found it advisable not to prepare either of 

 the above mixtures until needed because the formalin, which is a 

 reducing agent, causes much of the mercuric salt to pass over 

 into the insoluble mercurous salt. 



Gilson's Mercuro-Nitric Mixture, see 15. 



Hermann's Fluid, see 26. 



Kleinberg's Picro-Sulphuric, see 25. 



Lavdowsky's Mixture, see 18. 



Merkel's Fluid, see 12. 



Miiller's Fluid, 8. 



20. Osmic Acid (really the tetroxide of osmium OsO 4 ). 

 Osmic acid kills quickly and fixes well. It is exceedingly vola- 



