The research described in this book arose, in large part, from a sense
of frustration. For a number of years I had been studying the physiology
of the spinocervical tract, a somatosensory pathway, in the cat's spinal
cord. But I did not know, precisely, where the cells of origin of the
tract were located and therefore did not know what they looked like or
whether there were any correlations between structure and function. It
was true that electrophysiolo- gical experiments had indicated their
probable situation in the dorsal horn, and anatomical work had described
the morphology of cells that were likely to give rise to the axons of
the tract; but this was not satisfactory. With the publication, by
Stretton and Kravitz in 1968, of the Procion Yellow ionophoretic method
for intracellular staining, a new tool became available for studying the
morphology of physiologically identified neurones. We used the
techniques and, although very pleased with the beautiful appearance of
the dendritic trees of neurones seen in the fluorescence microscope, we
were again frustrated, this time by the inability of Procion Yellow to
stain axons for any considerable length. Therefore, P. K. Rose and P. J.
Snow and I began to try to develop a method that would stain the axon,
together with its collaterals, in addition to the soma and dendrites of
an intracellularly re- corded neurone.
