CoGHiLL, Stnictiire of the Nerve Cell. 193 



substance, at least in the adult, is opposed by van Durme, who 

 believes that the tigroid substance is derived from the nucleo-albumins 

 of the lymphocytes. 



Van Gehuchten ('97), accepting the reticular structure of the 

 ground substance, believes that the tigroid substance accumulates at 

 the nodal points of the net. These accumulations enlarge in certain 

 regions and form masses which ap})ear homogeneous when they be- 

 come sufficiently dense to obscure the reticular framework. A mesh 

 of the reticulum which remains unfilled produces a vacuole. Van 

 Gehuchten attributes the formation of these bodies to the affinity of 

 the protoplasmic net for a special chemical substance. It is, there- 

 fore, the form and disposition of the cytoplasmic net that determines 

 the size and distribution of the tigroid bodies ; and this, in turn, is 

 governed by the function of the neurone. 



Scott ('99), on the contrary, argues that the shape and distribu- 

 tion of the tigroid bodies are determined by the modification in the 

 shape of the cell during growth. The tigroid substance diff"usely per- 

 meates the whole cytoplasm in the early history of the cell. But the 

 growth of the cell and especially the development of the protoplasmic 

 processes break the substance up, by a purely mechanical process, into 

 separate bodies. The distribution of these bodies would seem, there- 

 fore, to be governed by the proportions and shape assumed by the 

 cell. 



Scott takes the position, furthermore, that the tigroid substance 

 cannot be considered as a part of the cytoplasmic net since it diffuses 

 into the cytoplasm after the net is formed. Though the two substances 

 may be intimately associated, they are structurally distinct. He con- 

 siders that the granules are homogeneous and that appearances to the 

 contrary, including vacuoles, are to be explained by irregularities in 

 their surfaces. 



In Lophitis Holinigren ('99) finds that the tigroid body may be 

 resolved into two constituents : a homogeneous ground substance, 

 which stains bluish gray in iron haematoxyiin and which tends to stain 

 in both colors with toluidin-erythrosin ; and granules which are sus- 

 pended in the ground substance and which stain black in iron haema- 

 toxyiin and deep blue in toluidin-erythrosin. The ground substance 

 forms in areas of varying shape and size and the granules may be dif- 

 fusely distributed through it or massed into solid bodies of different 

 proportions. Holmgren does not discover any definite relation of 

 these bodies to a formed ground substance of the cytoplasm. 



Although the substance occurs in comparatively small amounts in 



