Dear Sir:
—Permit me to make a brief explanation regarding the kind criticism offered by Prof. Osler, of Philadelphia, in Vol. V, No. 3, of the Journal.In the broad sense of the term, a hydatid tumor means simply a cyst or bag filled with a watery liquid. As we have hydatid tumors resulting both from the echinococcus and cysticercus, I defined in the very beginning of my paper the meaning I attached to the term as used in this paper, which was "the intra-cranial occurrence of either the echinococcus or cysticercus cellulosæ in man." In no way could my paper be construed as confounding these two parasites, for I distinctly described each briefly, under divisions A and B (see page 1, Vol. V, No. 1, of the Journal), and recognized them as two separate species of the same genus, but producing similar pathological changes when they invade the human