A LABORATORY OUTLINE OF NEURO-ANATOMY 361 



reagent. In a section prepared by this method the normal myelinated fibers are light 

 yellow, while the degenerated fibers are represented by rows of black dots. 



30. The newer silver stains, including the Cajal method and the pyridin-silver technic, 

 depend upon the special affinity for silver nitrate possessed by nerve-cells and their 

 processes. After treatment with silver nitrate the tissue is transferred to a solution 

 of pyrogallic acid or hydroquinon which reduces the silver in the neurons to a metallic 

 state. Nerve-cells and their processes are stained yellow or brown by these methods. 

 Myelin sheaths remain unstained. The axis-cylinders of the myelinated fibers are 

 light yellow, the unmyelinated axons are dark brown or black. The neurofibrils are 

 stained somewhat more darkly than other parts of the cytoplasm. 



31. The Golgi method furnishes preparations which demonstrate the external 

 form of the neurons, and make it possible to trace individual axons and dendrites for 

 considerable distances. The method also stains neuroglia. It is selective and rather 

 uncertain in its results, since only a small proportion of the nerve-cells are impregnated 

 in any preparation. The stain is due to the impregnation of the nerve-cells and their 

 processes with silver. 



32. The best stains for demonstrating the tigroid masses or Nissl bodies are 

 toluidin blue and Nissl' s methylene-blue. Both are basic dyes; and in properly fixed 

 nervous tissue they color the tigroid masses as well as the nuclear chromatin of nerve- 

 cells blue. 



THE PERIPHERAL NERVOUS SYSTEM 



33. The Spinal Ganglia. Study a longitudinal section through a spinal nerve and 

 its roots, including the spinal ganglion, stained by the pyridin-silver method. How 

 are myelinated and unmyelinated axons stained by this method? What kinds of cells 

 do you find? Study their axons. (See Figs. 39, 40 and pp. 62-66.) Look for the 

 bifurcation of the myelinated and unmyelinated fibers. Note the differences in 

 composition of the ventral and dorsal roots. What becomes of the various kinds of 

 fibers when traced peripherally? When traced toward the spinal cord? What is the 

 origin of the unmyelinated fibers? 



34. Study the vagus nerve of the dog in osmic acid and pyridin-silver preparations. 

 How are the various kinds of nerve-fibers stained in each? How does the structure of 

 the vagus differ from that of a spinal nerve? 



35. Study the cervical portion of the sympathetic trunk, which in the dog lies in a 

 common sheath with the vagus. Of what kind of fibers is it composed? What is the 

 origin and termination of these fibers? (See pp. 345-347.) 



36. Study the pyridin-silver preparation from the superior cervical sympathetic 

 ganglion. What is the source of the fine black fibers, and where do they end? Study 

 the ganglion cells. What becomes of their axons? (See Figs. 251, 253 and pp. 341-344.) 



THE SPINAL CORD 



37. Review the development and gross anatomy of the spinal cord (p. 42 and pp. 

 73-78). Examine the demonstration preparations of the vertebral column, showing 

 the spinal cord exposed from the dorsal side. In these preparations study the meninges 

 and ligamentum denticulatum, as well as the shape and size of the spinal cord. Note 



