66 



done as rapidly as possible, and if done rapidly, the air will be retained 

 in the lacunae and canaliculi, and cause them to stand out as black 

 spots and lines. If soft balsam were used it would soon drive out 

 the air, and being of nearly the refractive index of bone, it would 

 obliterate the lacunae and canaliculi. Further, if the hot balsam 

 were not cooled quickly, the air would be driven out and balsam 

 would take its place in the spaces. 



MUSCLE. 



188. Fresh. Much of the investigational work on muscle 

 has been done on fresh muscle, or frozen sections. For examination 

 fresh it is advantageous to have very thin muscles. Of the several 

 muscles that have been recommended, one of the most available is 

 the M. cutaneus pectoris of the frog. This may be prepared by 

 cutting the skin in the midventral line, cutting at right angles to 

 the first cut across to the angle of the jaw, thence caudally parallel 

 to the first cut. The skin flap so formed contains the insertion of 

 the muscle which may now be easily dissected free and removed to- 

 gether with some of the tissue at insertion and origin to handle it by. 

 It may be used for examination fresh, with the polarization micro- 

 scope, etc. 



189. Isolation Methods. Nitric acid ( 44) may be used for 

 plain muscle and for skeletal muscle. Potassium hydroxid ( 45) 

 is suitable for heart muscle. 



(a) Nitric acid. Place in the nitric acid dissociator the fresh 

 striated muscle, gland or organ containing the muscle, (plain 

 or striated,) that it is desired to isolate. If it is the intention 

 to w^ork out the anatomy of the muscle or the relation of the muscular 

 coats in an organ, the entire muscle or organ should be taken; other- 

 wise, portions will suffice. At the ordinary temperature of the 

 laboratory the dissociating action will have been sufficient in from 

 1 to 3 days; test at intervals with needles to ascertain whether 

 the fascicles and fibers can be easily separated; or fragments may 

 be shaken in a test tube or vial with water in order to separate the 

 fibers. 



When the dissociation is sufficient pour off the acid and wash 

 the muscle gently but thoroughly with water. If the tissue is to be 

 stained with hematoxylin or carmine, or kept for any length of time, 

 drain off the water and add a half -saturated solution of alum. For 



