The original observation of the existence of axon hillocks in neurons appears to have been made independently by two investigators nearly half a century ago. Simarro's (1890) description of the hillock was inaccessible to me in the original, but Cajal ('09) credits him with having observed this structure. I n this event, to Simarro belongs the priority of discovery. Schaffer (1893) reported that only one process of the nerve cell lacks chromophil substance and appears to be entirely homogeneous, smooth and of even contour. Furthermore, this process was said to take its origin from a homogeneous, pale, conical portion of the cell body. Cajal ('09) described the implantation cone as a region of the cell body in which the protoplasm is free from chromophil material and is in continuity with the axis cylinder ; the latter is likewise colorless when stained by Nissl's method. Both Schaffer and Cajal studied large spinal multipolar neurons, Betz cells and spinal ganglion cells. I n addition, the latter investigator included cells of the uncinate gyrus in his study. Neither author referred to the smaller, associational neurons of the spinal cord. Both failed to state the number of cells observed and the methods used in studying them. It was not indicated that individual cells were followed through serial sections in order to secure a complete and true picture of the cell as a whole.
l Contribution no. 284. Submitted in partial fulfillment of requirements for the degree, Master of Science. Research directed by W. F. Windle.