264: The Development of the Neuroglia 



and elaboration of the nerve-elenients and blood-vessels, the arrangement 

 being finally maintained only in the, then thin, ependymal layer. With 

 the beginning of medullation (pigs of IG to 20 centimeters) the syncy- 

 tium becomes moulded in the interspaces of the neurones and blood- 

 vessels and, for the lirst time, there begin to appear in the white sub- 

 stance the characteristic shapes hitherto described as neuroglia cells. 



13. The silver method cannot be trusted to tell the true story, and 

 never the Avhole story. As to the pictures of neuroglia cells obtained 

 by this method, while most of them probably contain nuclei, many of 

 them do not. 



14. The development of neuroglia fibers from the syncytium is a pro- 

 cess of transformation. Only fitlly developed (chemically transformed) 

 fibers react to the sjjecial neuroglia stain. These do not appear in pigs 

 till after the processes of medullation are well underway. The method 

 of their develojDment is somewhat similar to that described for the fibrils 

 of white fibrous tissue. 



15. In the early embryo all the nuclei are of the large vesicular type, 

 and the various varieties of neuroglia nuclei described in the literature 

 may be considered as transition forms of this type. Beginning with this 

 type, many of them gradually decrease in size, change in their staining 

 properties and, in their final stage, undergo fragmentation and disappear. 



16. The sjmcytium of the spinal cord digests in common Avith the 

 connective-tissue syncytium. Owing to the chemical effect of the diges- 

 tion process upon the tissue, and the presence of white fibrous tissue in 

 the specimen, and to the physical nature of the preparation, it is difficult 

 to determine whether neuroglia fibers digest or not. The framework of 

 the medullary sheaths in the central nervous system both resist diges- 

 tion and stain as white fibrous tissue does. 



17. About the medullating axones of the central nervous system there 

 occur cells similar to the nerve-corpuscles described in the developing 

 peripheral nerves. 



BIBLIOGRAPHY. 



Altmann. — Ueber Embryonales Wachstum. Leipzig, 18S1. 



Ada^iiciewicz. Albert. — Die Nervenkorperchen. Bin neuer, bisher unbekann- 



ter morphologischer Bestandtlieil der peripherischen Nerven. Sitzb. 



der Kais. Akad. der Wissensch., Bd. XCI, Abth. Ill, Marz Heft, 1885. 

 Aguerre. J. A. — Untersuchungen iiber die menschliche Neuroglia. Archiv 



fiir Mikros. Anat., Bd. LVI, 1900. 

 Capobiaxco. Fr.. and Fragnito, O. — Nuovo ricerche su la genesi ed i rapporti 



mutiii degli elementi nervosi e neuroglici. Annali di Nevrologia, 



Vol. XII, 1898. 



