^∗ ‘Lancet,’ Dec. 26, 1852, p. 588.Google Scholar

^∗ ‘Glugow Medical Journal,’ No. i., 1853.Google Scholar

^∗ It was at the strong recommendation of Professor Aitken that I was induced to take up the question of the specific gravity of the brain in the insane, as a method of investigation which promised to yield some definite, and valuable results.Google Scholar

^† ‘Brit, and For. Med.-Chir. Review,’ January, 1853, p. 240.Google Scholar

^‡ It must not be forgotten, however, that the majority of his cases also suffered from fever, as this seems to have a marked influence upon the specific gravity of the brain.Google Scholar

^§ ‘Edin. Month. Jour, of Med. Sc.,’ Oct. 1854, p. 289.Google Scholar

^∗ January, 1855, p. 207, ‘Brit, and For. Med.-Chir. Review.’Google Scholar

^† ‘Trans, of Patholog. Soc.,’ vol. xii (1860–61), p. 27.Google Scholar

^∗ In Dr. Sankey's original description he has stated it the reverse way, thus, he says that in a solution of the density of 1.050 the 1.051 head would float, and that marked 1.049 would sink. This, of course, was an oversight; but as he made a statement of this kind twice, it seems desirable, for the sake of clearness, to notice it.Google Scholar

^∗ To do away, as mach as possible, with this source of error from air bubbles, it is also desirable that the solutions to be employed should be made at least several hours before they are used, to give time for the disappearance of the minute bubbles necessarily produced by the mixture and stirring of the fluids. Occasionally, soon after the due adjustment of the solutions, some of the lower beads may be found floating at the surface, being buoyed up by the accumulation and contact of some of these minute air bubbles. A few slight knocks with a glass rod will at once dislodge them, and allow the bead again to take up its proper position at the bottom of the glass.Google Scholar

^† There is a possible error to be guarded against of a most important kind, and that is the employment of inaccurate instruments; I have tested my beads by comparing results obtained with them, and with a carefully made hydrometer having a long open scale, and have always found them tally with one another. The ordinary cheap urinometers are sometimes most untrustworthy. One which I purchased for half-a-crown I found to be just seven degrees wrong; and Dr. Beale speaks as follows concerning them:-” As sold, these instruments are often nearly useless, in consequence of the carelessness displayed in their manufacture. Out of twenty instruments, I have found several differing as mach as ten degrees from each other.”Google Scholar

^∗ For the names of the varions convolutions, see Gratiolet's work, ‘Sur les Plis Cérébraux de l'Homme;’ or else an admirable memoir by Professor Marshall (‘Philos. Transact.,’ 1864, p. 501), “On the Brain of a Bushwoman; and on the Brains of two Idiots of European Descent.”Google Scholar

^† The results so obtained are not quite as perfect as could be desired, since it is impossible to take snch portions from the cerebellum without including along with the gray matter some small ramifications of the white substance. The sections were made in the situations indicated, because in these regions it was found that fragments agreeing as nearly as possible with one another could be most easily taken for examination-that is to say, fragments always containing about the same relative amount of admixed white substance. The fact, however (as will be hereafter seen), that in so many cases the white matter of the cerebellum has the same specific gravity as these other superficial portions, consisting mostly of gray matter, makes this slight admixture of far less consequence than it would be if, as in the cerebrum, the gray and white matter differed considerably in their respective specific weights.Google Scholar

^∗ This portion of the work was done in the Pathological Institute of Berlin, where, through the kindness and courtesy of Professor Virchow and his two assistants, Drs. Elebs and Colnheim, every facility was afforded me for carrying on these investigations, and I now most gratefully acknowledge my obligations to them. As the brains occasionally remained on the wooden trays for about half an hour after the ordinary pathological examination, before I could proceed to estimate their specific gravities, and these trays were sometimes wet, I made a few experiments to ascertain what amount of influence, if any, such a length of exposure to air, or contact with a wet tray, would exercise upon the specific gravity of the white and gray matter of the brain, and found that within this period these conditions appeared to exercise no appreciable influence whatever. Thus, white matter, after lying (even completely) in water for a period of thirty minutes, was found to have the same specific gravity as before immersion; and no change, either, was found in the specific gravity of the gray matter of the convolutions, after allowing portions of the brain, covered by the arachnoid, to remain for a similar period with this surface downwards, in contact with a thin stratum of fluid upon a wet tray—the portions of gray matter examined before and after being taken from what were nearly adjacent portions of the same convolutions. And with regard to the influence of the high summer temperature, no increase of density could be detected after such short periods of exposure, provided the con volutions were still covered by the arachnoid, whilst as far as the white matter was concerned it was always easy to take portions from beneath a surface which had been at all exposed. Alterations from atmospheric influence were also guarded against, as much as possible, by throwing a towel over the brain during these occasional intervals.Google Scholar

^∗ Whilst this paper has been going through the press, I have made some experiments in order to ascertain what amount of error can result from inattention to the temperature of solutions, and have been much pleased to find this so very insignificant when sp. gr. beads are employed, as to render attention to this point of little importance. Thus the compensating variation in the beads is such, that I have found, after adjusting a solution of sulphate of magnesia at a temperature of 60† Fahr., to a specific gravity of 1.028, the solution could be raised to a temperature of 84† Fahr, before the 1.027 bead sank midway in the solution; whilst, on the other hand, when the solution was cooled to 40† Fahr., the deviation was still less, since the 1.029 bead still remained at the bottom of the bottle. During these experiments a thermometer was kept in the solution, and due precautions were taken to prevent alteration in the density of the solution from evaporation. If the solutions, instead of being prepared at the temperature of 60†Fahr., have been adjusted to the beads at a time when the temperature of the weather is above or below this point, a little reflection will show that this of itself tends to diminish the small amount of possible error before alluded to, and so makes attention to temperature even of less importance.Google Scholar

^∗ Adding to the twenty-five Nos. I and II.Google Scholar

^∗ Since this was written, I have made two post-mortem examinations of persons who were laid in the prone instead of the supine position, almost immediately after death, and so allowed to remain during the interval of more than twenty-four hours intervening between the death and autopsy. Notwithstanding this reversal of important conditions, differences of a similar kind were met with between the specific gravity of the frontal and occipital gray matter. In these particular instances, in fact, the discrepancy happened to be very great, since in one case the specific gravity of the occipital gray matter exceeded that of the frontal by 004, and in the other (a case of general paralysis) by as much as 009.Google Scholar

^∗ This seems pretty conclusive evidence that the difference is for the most part independent of the degree of congestion, and due rather to histological structure, even were this not also rendered still more probable by recent observations of Mr. Lockhart Clarke. (‘Proceed, of Roy. Soc.’ vol. xii (1863), p. 716.)Google Scholar

^∗ I may again state here that in removing the gray matter from the occipital convolutions, it was always done with a knowledge of the fact of its lesser depth in this region, and that, accordingly, I always took extra care, and removed thinner slices in order to estimate its specific gravity in this situation.Google Scholar

^∗ It may well be that during the life of the individual, and the active nutritive changes going on in the part, that no absorption may take place, whilst such an effect may follow after death when there is nothing to interfere with or modify the ordinary physical laws.Google Scholar

^∗ ‘Philos. Trans.,’ 1861, and ‘Med.-Chir. Trans.,’ vol. xxxix.Google Scholar

^∗ There seems reason to believe that this is not the correct average of the seventy-three cases in which Dr. Sankey investigated the specific gravity of the gray matter-there must either have been a misprint, or some slight mistake made in estimating the average. At p. 242 (Brit, and For. Rev., 1853) he states the average of gray matter in the thirty-six males to have been 1.0353, and of the thirty-seven females 1.0349. The mean of these two numbers would give 1.0351 as the general average, and an examination of his table (i), p. 250, also makes it probable that this is the more correct average.Google Scholar

^∗ These numbers refer to the left side; the average on the right is even lower, being 1.0296.Google Scholar

^∗ In ascertaining the specific gravity of the gray matter by taking portions including its whole depth, to ensure accurate results capable of comparison with others, it is absolutely necessary that the gray matter should be cut off in little cubical blocks, or of some symmetrical form, so as in all cases to take the same superficial area of surface and deep strata. A portion removed from a convolution in situ, with shelving edges, would necessarily include an undue proportion of the specifically lighter superficial strata. Seeing that the difference between these upper and lower strata is as much as 004, inattention to this point would considerably modify the correctness of the results.Google Scholar

^∗ From some experiments which I have made, it would appear that the difference in density of these two portions depends to a great extent upon the different amounts of fluid which respectively enter into their composition. Thus, a slice about “ thick of a corpus striatum, including both superficial and deep portions, having been exposed on a tray for two hours to the influence of the atmosphere at a temperature of 71° Fahr. (20¾°C.), whilst another similar portion was immersed in water for the same time, the alterations in density were these—Google Scholar

Thus, the superficial portion increased in density twice as much as the deep by evaporation from exposure to the atmosphere, whilst by immersion in water the deep portion diminished in density twice as much as the superficial owing to an increased absorption of fluid. Of course, a part of this lowering of the specific gravity with both portions may have been due to an exosmosis of saline matter.Google Scholar

^∗ Loc. cit., p. 254.Google Scholar

^∗ And the total number of mules and females examined by Dr. Sankey, between the ages of twenty and thirty, was only nine.Google Scholar