TRANSACTIONS OF SECTION I. 753 
observations upon embryos in various stages of development led him to the 
conclusion that the fibres originated as strands of undifferentiated protoplasm 
extending between the neuroblasts of the spinal cord on the one hand and the 
developing myotonic cells on the other. At a somewhat later stage fibrille 
appeared in these strands, and still later a sheath was formed from mesoblastic 
tissue which surrounded and enclosed the group of fibrille. A more doubtful 
conclusion which might perhaps be drawn was that the original path was one 
along which impulses surged to and fro, and that consequent upon this use the 
fibrillary structure was developed as a more convenient substratum for the 
maintenance and extension of that function. 
Dr. Mann pointed out that nerve cells might be theoretically in one of three 
states—viz., separate units, or continuous with one another, or at one time con- 
tinuous and at another separate. In all embryos at a certain period the motor 
cells in the cord form a syncytium with scattered nuclei, an arrangement which 
later on becomes less and less marked, until in most cases the cells form separate 
units. Cells not derived from a common mother-cell are never in continuity. 
He pointed out that great care was needed in drawing conclusions from any 
preparations where such electrolytes as corrosive sublimate were used for pur- 
poses of fixation, inasmuch as all coagulation by electrolytes invariably leads to 
a very distinct fibrillar appearance. This is much less marked after the use of 
such non-electrolytes as osmium tetroxide or formaldehyde free from formic 
acid, At present, therefore, we are not in a position to make any assertions as 
to the existence or non-existence of fibrils in nerve cells or in tissues, 
Dr. W. B. Hardy also directed attention to the treacherous nature of the 
evidence of fibres and networks in cells. A fibrillar structure can be produced 
from a perfectly homogeneous solution of egg-white by fixing it with the 
ordinary reagents and staining it in the usual way. Again, if a concentrated 
viscous solution of egg-white be stretched between two points and then treated 
with the ordinary fixing reagents, it can be shown that the fibrils produced in it 
run longitudinally, and are connected by less prominent ones which run 
transversely. These fibrils must, of course, be purely artificial. 
_ Dr. H. K. Anderson emphasised the point that, though the neurones might 
be physically continuous, yet on the whole they must be trophically discon- 
tinuous. Experimenting upon very young animals, he had found that section of 
a postganglionic segment led to degenerative changes in the corresponding 
preganglionic segment. On the other hand, the converse was not true. As a 
further point against the view that the fibrille of a preganglionic segment were 
continued down into the postganglionic fibres, he pointed out that Langley had 
shown that the mode of termination of the preganglionic fibres in the sympathetic 
ganglia was not specific, since an ordinary motor nerve can be made to grow 
down to a sympathetic ganglion, and, terminating there in its own specific 
manner, could yet establish physiological continuity. 
Dr. E. Overton pointed out that it had been proved that the presence of 
sodium ions was an essential condition for the physiological activity of both 
muscular and nervous tissues; and, in the second place, it had been shown that 
both sodium and calcium ions were essential for the proper action of nervous 
interconnections, thus tending to prove that some third substance intervened 
between the two units—z.e., that there was discontinuity. 
Dr. W. MacDougall argued that the fact that motor neurones could not 
conduct backwards was the best evidence of discontinuity. Upon the same 
hypothesis depended also the simplest explanation of another typical characteristic 
of nervous activity—the effect of summation of weak stimuli. Moreover, the 
‘law of nerve habit’ was most difficult to explain, except on the assumption that 
there is some intermediate structure between successive nerve elements which 
offers a resistance to the transmission of impulses—a block, however, which can 
be overcome by the action of appropriate stimuli. 
Professor Langley, in replying on the whole discussion, suggested, among 
other points, that the strands of material described by Dr. Kerr in the develop- 
ment of nerve fibres might be simply connecting structures along which the 
1904, 30 
