100 The Neuroglia of the Spinal Cord of the Elephant 
cords, is capable of being seen with the unaided eye, showing as a thin 
blue margin when stained by the Benda method. It should here be 
inserted that in a series of preparations (to be mentioned below) of the 
spinal cords of developing pigs, neuroglia fibers do not begin to appear 
or do not stain by the Benda method, till after the myellation of the 
nerve fibers has begun. 
Like the other connective tissues of the body, it is probable that 
neurogha fibers, after they are differentiated as such, may still have the 
power of further growth, thickening, and expansion. If so, a continu- 
ous conversion of endoplasm into exoplasm must not be necessary for 
the process. 
5. Further changes to be noted occur in the neuroglia nuclei alone. 
A classification of these is difficult and unnecessary for they merely 
present one series of transitions or phases of activity. All nuclei with 
endoplasm about them are of the large vesicular type. Many without 
endoplasm are of this type also. The remainder show different phases 
of shrinkage, increased density in staining and perhaps very gradual 
karyolysis (f, g, h, 1, Fig. 4). 
The neuroglia is capable of growth after adult life is attained. It is 
capable of hypertrophy. The gliomatous tumors are considered to re- 
sult from this power. Exactly what type of the nuclei takes part in the 
process is unknown. In sections of such tumors, the large vesicular 
type predominates greatly, and Brodmann describes “ cells” possessing 
an unusually large amount of cytoplasm. Also, at need, neuroglia may 
take part in the formation of scar tissue. The connective tissues as a 
whole gradually increase normally with age after adult life is reached. 
“A man is as old as his arteries” or as the meninges of his central 
neryous system. If the above observations made from the spinal cord 
of a practically adult elephant have to do with phases in the formation 
of neuroglha fibers, it is probable that neuroglia also continues slowly 
to grow with the age of the animal. Observations made from adult 
material, however, are neither wholly adequate nor conclusive. 
To verify impressions obtained from the adult spinal cord as to the 
processes by which the neuroglia fibers are developed, the study must 
necessarily be transferred to the developing material. For this purpose 
a set of preparations is now nearly completed. The pig was chosen as 
the source of this material because of the greater ease with which a 
series of embryos of this animal may be obtained. The set of prepara- 
tions involves transverse sections from the cervical region of the spinal 
cords of a series of embryos and foetuses ranging from 5 mm. to 30 em. 
in length, and likewise from a suckling pig of two weeks and from the 
