l6 MICROSCOPICAL DIAGNOSIS. 



REAGENTS. 



In preparing specimens for the microscope it is necessary, in 

 many instances, to keep the specimen surrounded by a fluid, as near 

 as possible of the same nature as the fluid that bathes the tissues in 

 the body. These fluids are called the normal fluids. They are: 



1. Normal saline solution. It is prepared by dissolving 7.5 

 grammes of sodic chloride in 1000 c. c. of distilled water. 



2. Blood-serum. Obtained by allowing some blood to clot in 

 a flat vessel. 



3. The aqueous humor of the eye. 



4. lodized-serum. A few crystals of iodine are dropped into 

 fresh serum to preserve it; or, a quantity of amniotic fluid, obtained 

 from an embryo calf, may be substituted for blood-serum. It is not 

 highly recommended as a normal fluid. 



Dissociating fluids are fluids which dissolve, or partly dissolve, 

 certain parts of a tissue without affecting other parts, so that by 

 shaking or teasing the unaffected portions can be isolated. 



lodized-serum, of a light brown color, is generally useful. 



Chromic acid in weak solution, .02 per cent., is useful for isolat- 

 ing the nerve cells in the spinal cord. 



Osmic acid, .1 to i per cent., solution, is a dissociating fluid of 

 very general application. 



Mtiller's fluid is useful for the stomach and kidney. 



Sulphuric acid is used for isolating the cells of cornified 

 epithelium, nails, etc. The tissue is placed in the acid for a few 

 minutes when it is removed and washed in water to which a few 

 drops of ammonia have been added. 



Hydrochloric acid, 50 per cent, solution, is useful for isolating 

 the uriniferous tubules of the kidney. The section of fresh kidney 

 should be thin, and it should remain in the acid from ten to fourteen 

 hours, when it is washed in alkaline water. 



Caustic potash, 30 per cent, solution, is useful for the muscular 

 and nervous tissues. 



For softening bone, Dr. Seiler recommends the following: 



Chromic acid, i grain. 

 Nitric acid, (C. P.) 2 C. C. 

 Water, 200 C. C. 



In four or five days the bone will be soft enough to allow a fine 



