I am not aware, however, that this theory has ever succeeded in practice, either in the human species or in the lower animals, though frequently tried. Nature will work on her own plan, and will develop the bones of the fœtus, while in the womb, to a certain extent, providing she has the means to do so; and if these are withheld, she is very likely to suspend its development altogether, rather than send it forth imperfect. I have known cases where everything was withheld, for the whole period, that contained a particle of lime, and yet the child's bones were as hard at birth as in any other case; the material being, probably, taken from the bones of the mother, which might be thus weakened, and made liable to displacement, without any good result whatever. It is also a question whether such a course, supposing it to succeed, might not be dangerous in another way, by causing an imperfection in the child which its future growth could not overcome. I have known some cases where this practice appeared to have caused abortion from imperfect development, and several others in which there was too much reason to fear that the child was injured, though safely born. As this is, therefore, at best, a very uncertain and ineffective process, and is also, probably, dangerous to the mother or child, or both, it does not appear to me worthy of further attention, and I merely allude to it in order to make the present sketch of such means complete. The other means are such as do not interfere, in any way, with the natural processes, but merely prevent sensation or feeling at the time of delivery. _Mesmerism_ has been recommended, and, in some few instances, tried, for this purpose, but its success has either been so small, or its action so uncertain, that no dependance can be placed upon it, notwithstanding many persons assert its power. Opium and other powerful drugs have also been given, but so much of them is required, at that time, to produce a sufficient effect, that their use becomes dangerous. Other substances, in the form of _vapour_, or _gas_, have also been used, the effects of which only last for a short time, and are not, generally speaking, at all dangerous. Among them may be mentioned nitrous oxide, or _laughing gas_, carbonic acid, sulphuric ether, and chloric ether, all of which were first employed in severe surgical operations.