722 HISTOLOGIC TECHNIC 



fluid. For their further manipulation a dissecting microscope is useful, 

 though not essential. Two sharply pointed needles, mounted in wooden 

 handles, are to be used. 



The fragment of tissue is pinioned with the needle held in the left' 

 hand, and with that in the right the tissue is gently torn by a rhythmic 

 combing motion, being very careful to avoid squeezing the tissue between 

 the needle and the slide. With a little practice bundles of fibers, groups 

 of cells, etc., are readily isolated sufficiently to be studied under moder- 

 ate magnification. During the teasing, the fragments of tissue should 

 be kept well moistened, and are to be frequently inspected under low 

 magnification to determine the progress of the operation. When satis- 

 factorily prepared, a cover lass may be applied, and the preparation 

 examined under higher magnification. 



In applying a cover glass care should be taken to permit one edge 

 of the cover to first touch the slide while being held at an angle of 30 

 degrees to 40 degrees. If the cover is then gently lowered into place, the 

 air is forced out before the advance of the fluid, and the many air 

 bubbles which would otherwise be included are not found in the prepara- 

 tion. 



The method of teasing is particularly applicable to the study of the 

 connective, and peripheral nervous tissues. Collagenous fibers, elastic 

 fibers, fat cells, and nerve fibers are readily isolated in this way. If 

 desired, they may be stained by the addition of a drop of a solution of 

 methyl green, picrocarmin, etc. 



Chemical Dissociation. It is necessary to dissociate many tissues 

 by chemical means, either because of the firm union of the elements 

 composing the tissue or because they may be too delicate and fragile to 

 withstand the mechanical teasing. Epithelial cells, nerve cells, and 

 muscle fibers are readily macerated in this way. 



For the dissociation of muscle fibers small cubes (0.25 to 0.5 c.c.) 

 are placed for ten to thirty minutes in the following solution : 



Strong nitric acid 100 c.c. 



Potassium chlorate, sufficient to saturate. 



The fragments of tissue should be handled with glass rods. After 

 some minutes they begin to disintegrate at the surface, and should then 

 be transferred to running water, where they are left to wash from three 

 to twelve hours. The pieces of tissue are then transferred to a mixture 

 of equal parts of alcohol, glycerin, and water, and thoroughly shaken. 



