130 



129. For securing the best results in injecting the following 

 conditions should be observed : ( i ) A young but nearly mature, 

 lean animal is to be preferred. (2) Kill the animal with an anes- 

 thetic (chloroform; and leave it in the anesthetic at least half an 

 hour before beginning the injection ; do not, however, wait until 

 rigor mortis sets in. (3) Inject only the part desired, tying all an- 

 astomosing vessels and all vessels to other parts. Inject into the 

 artery of the part, leaving the vein open until nearly pure injection 

 mass escapes, then tie it and continue the injection until the part 

 feels hard and is the color of the injection mass. (4) When the 

 injection is finished cool the part injected by means of cold water, 

 ice, or snow. 



(5) Harden the injected tissue i 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. For sectioning the collodion method is usually preferable. 



130. Silvering blood vessels. Silver nitrate may be used 

 for coloring blood vessels, and thus differentiating them. See 147. 



CALCIFIED STRUCTURES, BONE AND TOOTH. 

 (A). Decalcification. 



131. For the purpose of investigating the soft structures of 

 tissues containing lime salts, such as bone, teeth, and calcified carti- 

 lage, it is necessary to remove the lime salts before sections can be 

 prepared in the usual way by a process known as decalcified tion. 

 Solutions of a large number of acids, combined or uncombined with 

 other substances, may be used as decalcifiers. Very satisfactory 

 are: (i) nitric acid, 3 c.c. ; 70% (67%) alcohol, 97 c.c., and (<?) 

 nitric acid, 5 c.c. ; saturated aqueous solution of (potash) alum, 50 

 c.c. ; water, 50 c.c. In the first formula the alcohol, in the second 

 the alum acts as a restrainer of the nitric acid. The first of these 

 formulas is, perhaps, better for bone ; the second has a more rapid 

 action and is possibly a better decalcifier for teeth. 



132. Directions for use. The tissue to be decalcified must 

 be first thoroughly fixed and hardened by one of the approved 

 methods, picric alcohol is quite satisfactory, and should be in 



