M. Léri has taken a similar view in a Report on the Senile Brain[10] presented to a recent congress of alienists and neurologists. According to him “the nuclei which surround some of the atrophying nerve-cells do not play the part of neuronophags.” In his monograph “La Neuronophagie,”[11] M. Sand elaborates the same view. He relies on his observation that “neuronophags are usually either devoid of protoplasm or display only a very thin layer of it. They never exhibit protoplasmic outgrowths, and they never have granules in their cellular bodies (p. 86).” Still more recently MM. Laignel-Lavastine and Voisin[12] have taken the same view, maintaining that the neuronophags do not display phagocytosis. Although I cannot undertake here to give a detailed reply to the arguments of my critics, I may point out a fallacy that vitiates their reasoning. The study of the intimate structure of nervous tissue involves the treatment of that very delicate substance by numerous active reagents. It is extremely important not to forget the possibility of alterations which may be produced in the processes of preparation and which are extremely difficult to avoid. A glance at the figures given by my critics shows me that the neuronophags in their preparations had been subjected to violent treatment. When M. Léri speaks of “the nuclei which surround some of the nerve-cells,” and M. Sand of “cells without protoplasm,” it is clear that they had been observing cells destroyed by the processes of the laboratory. The illustrations in the memoir of M. Marinesco show that in his preparations, too, the neuronophags had been very greatly altered. It is well known that nuclei do not exist free in tissues, and that when they appear devoid of protoplasm, there has been some defect in the technical methods of preparing them for examination. As a matter of fact, neuronophags do not consist of nuclei with at the most a pellicle of protoplasm; like other cells, they have protoplasmic bodies which, however, are frequently destroyed by the violent processes of histological preparation. The arguments of my critics recall to me the words of a medical student, who, on being asked to describe the microbe of tuberculosis, said that it was a little red bacillus. The bacillus in question, like most bacilli, is colourless, but it is usual to stain it so that it may be visible under the microscope. The student, knowing it only in particular preparations, had a false idea of its appearance. In well-made preparations, neuronophags are typical cells with abundant protoplasm. When they have been preserved by a process that does not dissolve their contents, they show granules like those found in nerve-cells.