25G The Development of the ISTeuroglia 



It is true that in the adult also, where blue-staining fibers are abund- 

 ant, both unstained fibers and fibers showing some of the above features 

 may be observed. Whether such appearances in the adult indicate im- 

 perfect staining or the development of new fibers, is difficult to say. 

 Probably they indicate both. But when found in a stage before which 

 no fibers have taken the neuroglia stain, the question is somewhat dif- 

 ferent. There are evidences that the process of both development of fibers 

 and transformation does continue into the adult stages. 



In the field chosen in Fig. 13 (suckling pig of two weeks) the con- 

 ditions resemble those in the adult. Throughout the section, however, 

 neuroglia fibers are not so abundant as they are in the adult. On the 

 other hand, fibers in the process of transformation may more often be 

 seen and nuclei surrounded by the more deeply staining protoplasm, are 

 considerably more numerous than in the adult. Whether in the young 

 or the adult, a fully transformed (staining) neuroglia fiber usually 

 appears in a clearer space, as though the surrounding substance had been 

 used up in its development. 



The field represented in Fig. 13 was chosen chiefly because of the types 

 of nuclei contained in it. Medullation is far advanced. Either due to 

 an increase in pressure upon the substance in the interspaces consequent 

 to the enlargement of the axones by medullation or due to some chemical 

 difference, or fault in technique, the masses of more deeply staining 

 protoplasm, when present, color somewhat darker than in Fig. 12. 

 Nuclei present in these masses give them the semblance generally de- 

 scribed as neuroglia cells. When an interaxone space is large enough, 

 it may contain two or more nuclei. The mass indicated by a in Fig. 13 

 both illustrates and explains the " multinucleated neuroglia cells " de- 

 scribed in the literature (Krause, Brodmann, Aguerre). Were the 

 axone in the center of this mass removed, the type would be perfect. 

 As it is, it gives the appearance of three closely joined cells. It must 

 be remembered that most of the studies of neuroglia cells have dealt 

 wdth the tissue as found in the white substance rather than in the gray, 

 where the different arrangement and less abundance of axones render the 

 usually described form difficult to find. 



N'uclei surrounded by the more deeply staining form of the syncytial 

 protoplasm are always of the large vesicular variety. Both because of 

 this and because of the fact that for quite a period of the embryonic 

 development all the nuclei are of this type, the large vesicular nuclei 

 are considered the more primary or least modified form. There may be 

 seen nuclei with the more deeply staining substance partially converted 

 (c. Fig. 13) and free nuclei (d). Free nuclei may be of the vesicular 



