288 REAGENTS AND PROCESSES 



alga is submerged for a few seconds in a mixture of one part of 

 sea-water with two parts of fresh water in which has been dis- 

 solved sufficient ferrocyanide of potassium to give it the specific 

 gravity of sea-water. The alga is then rapidly rinsed in sea- 

 water and placed for about two seconds in a mixture of two parts 

 of sea-water and one part of fresh water, to which has been added 

 a few drops of freshly prepared ferric chloride. This produces 

 in the membranes of the alga a precipitate of Berlin blue. The 

 alga is then transferred to sea-water for further growth. In 

 case new lamellae are added to the membranes, the new portions 

 will appear colorless, while the older portions will appear blue 

 because of the Berlin blue which was precipitated in them. 



Bismarck Brown. — This is preeminently a nuclear stain. 

 The powder is soluble with difficulty in water. It is a good plan 

 to treat with boiling water and after a day or two to filter. Or a 

 saturated solution may be made in 70 per cent, alcohol. Al- 

 though Bismarck brown stains rapidly, it does not overstain. 

 It may be used for staining in Mo or for staining sections on the 

 slide. 



Boracic Acid. — Used as a mounting medium for sections 

 containing mucilaginous membranes. The sections are cut 

 from dry material and placed in a 10 per cent, solution of neutral 

 lead acetate to harden the mucilaginous layers. Then the sec- 

 tions are stained in a solution of methyl blue, washed in water, 

 and mounted under a coverglass in a 2 per cent, solution of 

 boracic acid. The coverglass should be sealed down with a 

 mixture of paraffin and vaseline, which is applied with a brush 

 while melted. 



Borax-carmine. — A 4 per cent, solution of borax in water 

 is made and to it is added 3 per cent, of carmine; an equal bulk 

 of 70 per cent, alcohol is then added to this. The mixture is 

 left standing for a day or so and then filtered. Sections should 

 lie in the stain for about twenty-four hours, and should then 

 be transferred without previous washing to acidulated alcohol, 

 made by adding four drops of hydrochloric acid to 100 c.c. of 

 alcohol. Here they should remain until they become bright 



