FASCICULUS CEREBRO-SPINALIS IN THE RAT 



419 



interrupted, medullated and non-medullated stretches succeed- 

 ing each other along the course of the same fiber. In any case, 

 the medullation of the pyramidal tract in the white rat is incom- 

 plete, and such sheaths as are present are very thin. It is not 

 possible to draw the same sharp line between entirely non-med- 

 ullated and fully medullated fibers that can be drawn in the 

 spinal nerves. 



Fig. 8 An area from the fourth thoracic segment of the spinal cord at the 

 boundary between the pyramidal, a, and the cuneate, 6, fasciculi; only axons arc 

 shown. Ocu. 3, Obj. 2 mm. 



Fig. 9 An area from the fourth thoracic segment of the spinal cord at the 

 boundary between the pyramidal, a, and the cuneate, h, fasciculi; the myelin 

 sheaths are shown. Ocu. 3, Obj. 2 mm. 



The same results are given by both the old Weigert and the 

 Pal-Weigert methods. Care has been taken not to decolorize 

 the smallest myehn sheaths. To avoid this, sections 8 to 10 /x thick 

 were used, and the decolorization was stopped just short of com- 

 pletion, leaving a diffuse light blue tint in the background. In 

 these thin preparations it was possible to see dark blue myehn 

 sheaths clearly outhned against the lighter background. The 

 number of sheaths seen in this way corresponded with the num- 

 ber seen in the more fully differentiated preparations. When a 

 well differentiated preparation is stained with acid fuchsin a 



