262 The Microscope. 



6. Dissociation in nitric acid. In order to get good results it 

 was found necessary to put the specimen into the reagent directly 

 after death and the removal of the skin. A twenty per cent, 

 solution of nitric acid (cone, nitric acid 20 cc, water 80 cc.) softens 

 the connective tissue, the time necessary varying with the tempera- 

 ture, being 24 h. if below 18^ C, and 1 h. if 40-50° C. Above 

 40° C. frequent examination is necessary to avoid too great disin- 

 tegration. The acid is removed by placing the specimen in water 

 for one-half to 24 h. A few fascicles of a muscle are placed on 

 a slide, in glycerine containing picric acid or picro-carmine which 

 gives a general stain, and gently dissected with coarse needles; the 

 excess of glycerine is removed; a drop of warm glycerine jelly is 

 allowed to spread slowly over the preparation; the fibers are 

 arranged with the needles so as to lie as straight as possible; the 

 slide is cooled until the jelly has a glutinous consistency and then 

 is covered by a warm cover or one thinly coated with warm glycer- 

 ine jelly. In this way the fibers retain their places on the slide. 



If the specimen was put into the acid in toto, so that the 

 muscles were held naturally extended, only a slight shrinkage took 

 place in their length, but if a detached muscle was put into -the 

 acid a shrinkage of one-third its length was observed. In both 

 cases the dissected fibers were somewhat longer than the shrunken 

 muscle from which they were taken, probably owing to the fact that 

 the connective tissue shrinks more than the fibers, and draws the 

 ends of the muscle together. 



It was found possible to stain the nuclei after dissociation in 

 the acid if, after thoroughly removing the acid by water, the muscle 

 was placed 12 h. in Koch's dilute, red, tubercle stain. After stain- 

 ing, a few fascicles are placed .on a slide with 20 per cent, alcohol 

 and a drop of picric acid to give a general stain; this was replaced 

 by 50 per cent, alcohol and then by 95 per cent. In the last the 

 fibers, which in the 20 per cent, alcohol are stiffened, again are 

 flexible and easily dissected by needles. Clove-oil collodion is 

 then placed on the specimen and partially dried to hold the fibers 

 in position, and it is then mounted in Canada balsam. Though this 

 stain is excellent at first, it was found that after two months some 

 of the specimens were much faded. 



Prof. Gage has recently found that by placing muscles after 

 being freed from nitric acid by soaking in water, in a saturated 

 aqueous solution of alum, the fibers, for some weeks at least, can be 

 dissected as well as when first prepared. The nuclei stain well in 

 hsematoxylin. 



