366 Journal of Applied Microscopy. 



it MerkeFs Fluid. — Equal volumes of a 1.4 per cent, solution of chromic acid 

 and a 1.4 per cent, solution of platinic chloride. This is also an expensive 

 reagent. It is recommended for mitotic phenomena, but does not seem to equal 

 Flemming's solution. 



c. Hermann's Fluid. — 



1 per cent, platinic chloride, 15 parts. 

 'Glacial acetic acid, 1 part. 



2 per cent, osmic acid, 4 or '1 parts. 



This is the most expensive fixing agent yet discovered, and for botanical 

 purposes it does not seem to be any better than the cheaper chromic mixtures. 

 It is mentioned here with chromic mixtures because it originated as a variation 

 of Flemming's fluid, the platinic chloride being substituted for the chromic acid. 



According to Lee, the chief objection to all mixtures into which chromic acid 

 enters is that *• it precipitates certain of the liquid albuminoids of the tissues in 

 the form of filaments or network, which are often of great regularity and simu- 

 late structural elements of the tissues.'' Nevertheless, the mixtur'es which have 

 just been described are the best which have yet been thoroughly tested. If 

 material killed in any of the above mixtures is not well washed, the hcematoxy- 

 lins will not stain. It is claimed that the anilins will stain in spite of poor 

 washing, but it is a question whether such preparations are as permanent as 

 those from well washed material. 



PICRIC ACID. 



Use a saturated solution in water or 70 per cent alcohol. One gram of 

 picric acid crystals will saturate about 75 cc. of water or alcohol. This reagent 

 penetrates well and does not make the material brittle. It is to be recommended 

 when difficulty is anticipated in the cutting. If used cold, the time varies from 

 one to twenty-four hours, depending upon the character of the tissue and size of 

 the specimen. If used hot (S5 degrees C), five or ten minutes will be sufficient. 

 Material should be washed in 70 or 50 per cent, alcohol. Water is injurious, 

 and some even go so far as to avoid aqueous stains unless the material has been 

 thoroughly washed. The washing should be continued until the material appears 

 whitish, and the alcohol no longer becomes tinged with yellow. Picro-carmine 

 gives its best results after this reagent. Picric acid can be combined with 

 various other fixing agents, and so we have picro-sulphuric acid, picro-nitric acid, 

 picro-chromic acid, picro-chromic-sulphuric acid, and picro-osmic acid. 



CORROSIVE SUBLIMATE. 



Use a 2 to 5 per cent, solution in water, or 70 per cent, alcohol. The 

 addition of about 1 cc. of glacial acetic acid to 100 cc. of this solution is certainly 

 an improvement. The time required is considerably shorter than for chromic 

 solution. From one to ten hours will be found to be sufficient. If used hot 

 (85°C.) only five or ten minutes is required. Washing may be done with water, 

 but 50 per cent, alcohol is better. If a few drops of an iodine solution be 

 added to the alcohol, the alcohol takes on a brownish color, but soon clears up. 

 If the addition of iodine be continued, the washing is complete when the 

 alcoliol no longer clears up, but retains the brown color. If the washing is 



