83 



(5) Harden the injected tissue 1 or 2 days in 50% alcohol, 2 

 or 3 days in 67% and 82% alcohols. The acidity of the alcohols 

 should be insured by adding to the 50% alcohol a few drops of acetic 

 acid. The tissue may be stored in 82% alcohol until ready for sec- 

 tioning. Formalin (10%) may also be used as the fixer and preserving 

 fluid. For sectioning the celloidin method is usually preferable. 



219. Silvering blood vessels. Silver nitrate may be used 

 for coloring blood vessels, and thus differentiating them. See 222. 



220. Dense Masses, such as do not pass through the capil- 

 lary network are useful in giving double injections, the veins and 

 capillaries one color, arteries another. Two such may be mentioned: 

 (a) Lampblack Gelatin Mass; (b) Ultramarine Gelatin Mass (Spal- 

 teholz.). 



(a). Lampblack and gelatin mass in the proportion of about 

 1:12. 



(b). A 10% gelatin mass to which is added ultramarine in 

 proportion of 30:100. 



In injecting, inject through the artery with one of the gelatin 

 masses given in 216 , and follow it up with one of the above 

 which will push the first mass through into the capillaries and veins. 



SILVER NITRATE IMPREGNATIONS. 



221. The preparations stained by means of nitrate of silver 

 are prepared as follows; The fresh tissue is washed for a minute or 

 so in distilled water to remove from the surface all albuminous sub- 

 stance, and then transferred for 2 to 5 minutes or longer to a 1 to 

 Yf/o aqueous solution of silver nitrate and exposed to direct sunlight 

 until a light brown. When, by examination with the microscope, the 

 stain was found to be sufficient it was again rinsed in water and placed 

 in glycerin or alcohol. Employed in this manner with fresh tissue, 

 silver nitrate stains the cell cement, affording thus negative images of 

 the cells. If a membrane such as mesentery is to be silvered removed 

 from the body, it should first be cautiously stretched, as over a ring, 

 to avoid creases. 



222. Silvering Vascular Epithelium. In order that the 

 vascular epithelium of small arteries, veins, and capillaries should be 

 well demonstrated, silver nitrate solutions of J^ to / / 2% strength 

 must be injected into the vessels. 



