TRACT OF LISSAUER 117 



THE TRACT OF LISSAUER IN THE GUIXEA-PIG 



In the guinea-pig the tract of Lissauer is much hke that in 

 the rat. The substantia gelatinosa is excessively developed and 

 occupies a position near the surface in each of the three princi- 

 pal regions of the cord. The tract is even less developed than 

 in the rat, and is represented by a thin strip berween the sub- 

 stantia gelatinosa and the surface of the cord. In the seventh 

 cervical segment there is a lateral expansion of the tract similar 

 to that in the rat, but less well defined. In the thoracic and 

 lumbar regions the lateral expansion is less developed than in 

 the cervical segments. 



THE SUBSTANTIA GELATINOSA ROLANDI 



The intimate and constant relation of the tract of Lissauer 

 to the substantia gelatinosa and the interchange of fibers be- 

 tween the two suggests the possibility that the latter is the 

 nucleus of reception of the afferent fibers of the former. This 

 raises the question as to whether the structure of the substantia 

 gelatinosa is in keeping with such a conception of its function. 



According to all recent observers, nerve cells are very numerous 

 in the substantia gelatinosa Rolandi. Ziehen ('99) has given a 

 good summary of the literature on the nerve cells of this region. 

 Rosenzweig ('05) and Sano ('09) have reworked the subject with 

 the method of Bielschowsky. The larger cells of the zonal layer 

 (the most superficial layer of the substantia gelatinosa) are well 

 known. According to Cajal, their axons run into the lateral 

 funiculus. But the most numerous and most characteristic cells 

 are the small multipolar elements. These are very small, and, 

 according to Rosenzweig, the substantia gelatinosa is 'crammed 

 full' of them. All authors agree that they are demonstrated 

 with difficulty because of the instability of their protoplasm, 

 which is destroyed by the usual fixing and hardening agents. 

 Sometimes the nuclei of these cells alone are visible in such prep- 

 arations. In good Bielschowsky preparations (Rosenzweig) the 

 substantia gelatinosa contains dendrites in large quantity derived 



