The question of the specific gravity of the brain has already engaged the attention of several British investigators, the results of whose labours have from time to time been made known, but with the exception of a few isolated observations little has been done to this subject by continental anatomists or pathologists. At a time like the present, when the attention of scientific men is directed with renewed interest to all details concerning weight, form, and configu ration of the human brain, it seems reasonable to suppose that more complete observations upon the specific gravities of its several parts would be of itself a matter of scientific interest, independently of the importance attaching to the subject on account of the probable light which such an investigation might throw upon the situations of change in brain tissue, in connection with certain obscure forms of cerebral disease. The observations of previous inquirers have been directed to the estimation of the specific weights of the cere brum and cerebellum as a whole, of the gray and white matter separately, and of the combined central ganglia of the cerebrum. These investigations have been made by some, upon the brains of sane, and by others, upon those of insane individuals; and amongst the forty persons whose brains I have myself examined, there are also representatives of these two classes, though a large majority is included under the former denomination. Whilst tho actual number of brains inspected by myself is, therefore, limited, still the examination of their several parts has been more complete, so that this communication contains a record not only of differences found to exist in the specific gravity of gray matter taken from frontal, parietal, and occipital convolutions respectively; but, also, I believe for the first time, of the specific weights of the optic thalami, pons, medulla oblongata, and different parts of the corpora striata, taken sepa rately. Some of the facts so ascertained are very interesting, and seem to justify their early publication. Owing, also, to the existence of certain discrepancies in the results arrived at by preceding inves tigators and myself, it seems desirable that these discrepancies as well as our respective methods should be considered, with a view, if possible, of ensuring greater uniformity of results for the future. Investigations of a delicate nature such as these, when conducted by different observers, are comparatively useless for the purposes of comparison, unless some uniform method be adopted. These considerations have induced me to make known the results of my own observations sooner than I should otherwise have done, and will, I hope, be deemed a sufficient justification for my bringing them forward before they are sufficiently numerous to enable me to draw any very safe deductions from them. The present paper may, therefore, be con sidered as a first contribution towards the elucidation of a subject, at which I hope to work more thoroughly in the future.