MODERN METHODS OF EXAMINATION. 67 



2. CHEMICAL REAGENTS. 



The greatest care should be used with these, that the 

 instrument and glasses may be preserved. A small drop, 

 applied by a glass rod drawn out to a point to the edge of 

 the glass cover, will suffice in most cases. 



Sulphuric Add. Concentrated is used to isolate the 

 cells of horny structures, as hair, nails, etc. Dilute (1 part 

 to 2-3 of water) gives to cellulose, previously dyed with 

 iodine, a blue or purple color, and, when mixed with 

 sugar, a rose-red to nitrogenous substances and bile. 0.1 

 to 1000 of water, at a temperature of 35-40 C., resolves 

 connective tissue into gelatin and dissolves it, so as to be 

 useful in isolating muscular fibres. 



Nitric Acid. Diluted with 4 or 5 parts water, separates 

 the elementary parts of many vegetable and animal tis- 

 sues when they are boiled or macerated in it. With chlo- 

 rate of potash it is still more energetic, but caution is 

 needed in its use. 



Muriatic Acid, Strong. Used for dissolving intercellular 

 substance, as in the tubes of the kidney, etc. Dilute for 

 dissolving calcareous matter. 



Chromic acid, J to 2 per cent, solution for hardening 

 nerves, brain, etc. 



Oxalic add, to 15 parts water, causes connective tissue 

 to swell and become transparent, while albuminoid ele- 

 ments are hardened. Preserves well delicate substances, 

 as rods of retina, etc. 



Acetic acid makes nuclei visible and connective tissue 

 transparent, so as to exhibit muscles, nerves, etc., other- 

 wise invisible. 



Iodine (1 grain of iodine, 3 grains iodide of potassium, 

 1 ounce of water) turns starch blue and cellulose brown. 



Caustic potash or soda renders many structures trans- 

 parent. 



