

SPINAL COED 229 



Embryological study has shown also that the medullary sheath 

 appears at different periods of development in the different tracts 

 of nerve-fibers, although the time is constant for each particular 

 tract. The presence of the sheath in certain tracts, and its absence 

 in others, makes it possible to outline the tracts in a series of 

 embryonic cords. 



Physiological experiments demonstrate the functions belonging 

 to certain tracts. 



PRACTICAL DEMONSTRATION 



Nerve-tissue should, under all circumstances, be hardened in Miiller's 

 fluid. The cord should be obtained as nearly fresh and uninjured as possi- 

 ble, cut transversely with a sharp razoj 1 into pieces a centimeter long, and 

 placed immediately in the fluid in the proportion of a liter of the mixture 

 to 100 grams of tissue. The solution should be thrown away after twenty- 

 four hours, and a fresh supply provided. It should be again changed after 

 three days, and again after another week. After four weeks the bichromate 

 should be poured off, and the tissue rinsed once with water, after which 

 the hardening is to be completed with alcohol in the ordinary manner. 



After hardening, pieces from the different regions should be cut, and 

 this is best effected after imbedding. Transverse sections are the most[ instruc- 

 tive, although the student should afterward study longitudinal sectiobs. The 

 sections may be stained with hsematoxylin and eosin. Sections should also 

 be stained by the Weigert-Pal method. For this purpose the hardening 

 must be done with great care, and must be continued longer. The pieces of 

 tissue are placed in alcohol direct from Miiller's fluid without washing. The 

 details of the method are given on page 30. The Golgi method presents too 

 many difficulties to be attempted by any but advanced students. 



HUMAN SPINAL CORD CERVICAL REGION TRANSVERSE 

 SECTION (Fig. 149) 



OBSERVE : 

 (L.) 



1. General arrangement of gray and white substance, with 

 the latter surrounding the former, which resembles in outline the 

 letter H. 



2. Subdivisions of white substance. (a) Anterior median 

 fissure. (Note its passage inward and its cessation before reach- 

 ing the gray substance.) (b) Posterior median fissure. (Note 

 its shallowness as a true fissure, and the extension of the connec- 

 tive tissue from the bottom inward, until the gray substance is 

 met. Compare the two median fissures.) (c) The emergence of 

 the anterior nerve-roots. (This provides the external or lateral 





