512 A. J. LINOWIECKI 



by Bischoff ('()()). No such precipitation occurs when the 

 pyi'idine-silver technique is used as outhned by Ranson ('12) and 

 as described in this paper, and the results are uniform, i.e., as 

 far as the staining of the material is concerned. 



The size of the fasciculus cortico-spinalis or pyramidal tract 

 varies with the different species. Schafer claims that it is directly 

 proportional to the number and complexity of the movements 

 which an animal is capable of executing (King '11). Thus the 

 pyramidal tract of sheep as found by that investigator (King) 

 is comparatively small and is composed of very fine fibers. Like- 

 wise Spitzka ('86) asserts that ''the intellectual rank, or what is 

 the anatomical index of such rank : preponderance of the highest 

 nerve centers is not the only factor in determining the size of 

 the pyramids. The dimension of the animal has undoubtedly 

 some influence." The tract of a rat whose extremities are used 

 very much, is found to be better developed (Bec'jterew '90). 

 He also says that this tract is no less or perhaps better developed 

 in cats and dogs, while in man and the primates the development 

 is at its height. The tract diminishes in size, however, as it 

 extends caudalwards. The fibers diminish rapidly in number 

 (King '11) and the tract disappears in many species before 

 reaching the lumbar region. To give a relative idea of the size 

 of the pyramidal tract in various species, v. Lenhossek ('89) 

 selected a certain same level of the cords in the different animals 

 and then letting the transverse area of this level represent 100 

 per cent, he expressed the area of the tract in terms of it. Thus 

 at the level of the middle of the cervical cord, the pyramidal 

 tract of the guinea pig occupied three per cent of the transverse 

 area of the cord ; in the rabbit, 5.3 per cent ; and in the cat, 7.76 per 

 cent. This would tend to prove the statement made above 

 about the factors governing the size o^ the tract. 



All of these investigators used the Weigert, Pal-Weigert, 

 Marchi, hematoxylin-eosin and other common stains and were 

 able to study only the medullated fibers. Not until the pyridine- 

 silver stain was utilized could the composite structure of the 

 pyramidal tract be noted. Thus in his paper on the pyramidal 

 tract in the albino rat, Ranson ('13) has shown that in addition 



