514 A. J. LINOWIECKI 



To bring out the myelin sheaths in the pyramidal tract, similar 

 pieces of cord were stained according to the Pal-Weigert technique 

 after fixing the denuded cord in Mtiller's fluid for one month. 

 The cut sections were from 12 to 22 microns in thickness, and 

 only those were utilized which were at the level of the junction 

 of the seventh cervical nerve roots with the cord. The exact 

 level of the sections was not determined in the case of the mole. 

 The entire cervical cord of one mole was prepared by the pyri- 

 dine-silver technique and cut into serial sections. Preparations 

 were also made from the thoracic and lumbar segments. 



OBSERVATIONS AND RESULTS 



Pyridine-silver preparations showed the pyramidal tracts of 

 the rat, guinea-pig and mole so clearly differentiated that no 

 question arose as to their topography. The non-medullated 

 fibers are stained very dark, giving the tract a dark brown ap- 

 pearance which differentiates it from the rest of the white sub- 

 stance. In these sections the contrast is greater than could 

 be obtained by the Marchi method, for in animals such as these 

 the enormous numbers of non-medullated fibers give the tract a 

 very characteristic appearance in the pyridine-silver preparations. 



In the sections of the spinal cord of the rabbit, cat and monkey 

 where the contrast is not very sharp, the results of other investi- 

 gators, who used the embryological and the degenerative methods, 

 were used to locate the tracts. In all cases the identification 

 of the tracts is based on the results of the older methods. The 

 pyridine-silver stain shows that the area which other investi- 

 gations have shown to be occupied by the pyramidal tract is 

 more or less sharply marked off from the rest of the white sub- 

 stance because of its large content of non-medullated fibers. 

 Only in those cases where, as in the rat and mole, these greatly 

 predominate, would the pyridine-silver method be of service 

 in tracing the bundle downward from the brain. 



