388 APPENDIX 



27. Osmic Acid. 



Use. — Kills living protoplasm — e. g., Protozoa, etc., in- 

 stantaneously ; fixes nuclei ; and stains fats and oil 

 black. 



Preparation. — Crystals of osmic acid come in small tubes, 

 each containing one gram. One of these tubes may be 

 broken in a bottle containing ninety -nine cubic centi- 

 metres of distilled water. This gives a one per cent, solu- 

 tion which may be diluted. The bottle should have a 

 ground - glass stopper and be kept in a dark place, or 

 wrapped with thick, opaque paper. 



28. Pasteur's Solutions. 



Use. — Culture-media for yeast, mould, spores of fungi, etc. 



Preparation. — The following formula for making the solu- 

 tion " with sugar " is given in Huxley and Martin's 

 " Practical Biology " : 



Potassium phosphate 20 parts 



Calcium phosphate 2 



Magnesium sulphate 2 



Ammonium tartrate 100 



[Cane-sugar] 1,500 



Water 8,376 



10,000 parts 



The solution " without sugar " is the same as the above 

 with the sugar omitted. 



29. PerenyVs Fluid. 



Use. — Kills small animals, eggs, etc., instantaneously. Ob- 

 jects may be left in it from two to five hours, then trans- 

 ferred to seventy per cent, alcohol for a day, then to 

 ninety per cent, alcohol. 

 Preparation. — Mix together four parts of a ten per cent, 

 solution of nitric acid, three parts of a one-half per cent, 

 solution of chromic acid, and three parts of ninety per 

 cent, alcohol. 



