Such appear to be the regular successive stages in the action of chloroform; but sometimes this regularity is interrupted; and the influence of the poison extends to all the nervous centres conjointly, or to those of the heart more especially, including, perhaps, the ganglia in the cardiac tissue; and sudden and unexpected prostration comes on, with a pale cold skin, sunken features, and a vanishing pulse. it is in such cases that death ensues almost instantaneously; the heart ceasing to beat from the direct action of the poison, and the patient dying of syncope. They are the cases most to be dreaded, as least likely to yield to remedial measures.

But what is it that directs the action of the poison thus exceptionally upon the heart? it is not, as some have imagined, any previous disease of that organ, or general debility, or antecedent disease of any kind; for the result has occurred much more frequently in the absence of these circumstances, and in conditions of perfect health. Dr. Snow infers from his experiments on animals that, if the atmospheric air inhaled is loaded with as much as 8 or 10 per cent. of the vapour, the chloroform is apt to act directly on the heart, and thus becomes exceedingly dangerous; while, if it contain only from 4 to 6 per cent. it may be inhaled with impunity; as the poison, in this state of dilution, shows no disposition to affect the circulation directly, but expends its action on the brain, and may always be regulated. But they who examine carefully the published accounts of speedy death from chloroform, will find that this explanation of Dr. Snow will not hold good; for the quantity used has often been so small, and the caution exercised so great, that the degree of concentration of the vapour could not possibly have approached the point which he considers fatal. The only explanation we have to offer is, that individual idiosyncrasy sometimes causes excessive susceptibility in the nervous centres of circulation, so that they sink under an amount of influence which is generally quite harmless; just as we sometimes meet with individuals who will suffer excessive salivation from a grain of calomel. This is extremely unfortunate; as it takes away the opportunity of employing preventive measures; but an important practical inference is, that chloroform should never be tried, a second time, in persons who have on any occasion exhibited this idiosyncrasy, and happily escaped from its consequences with their lives.

One other question remains to be solved in relation to the method of operation of chloroform. is it directly stimulant, as some have supposed, and indirectly sedative, or has it the property of immediately depressing the nervous centres on which it operates ? This is a question of great practical importance, the decision of which must frequently determine our course in relation to the use of chloroform. if we think it sedative, we should employ it under circumstances in which, as a stimulant, it would prove highly dangerous; and conversely, should avoid it when, in a similar supposition, it might be clearly indicated. The reader is already aware that I consider it directly sedative. Some reasons for thinking it so I have before given. The strongest are the symptoms of its action, which, so far as I have personally observed, are always those of general depression. I have already referred, in this relation, to the symptoms produced by it when swallowed. Those resulting from its inhalation are not less conclusive. The medicine is inhaled; and almost instantaneously is seen a depression of the sensorial functions, without, for the most part, the least sign of preliminary excitement, such as opium, alcohol, and ether always afford. There is, it is true, not unfrequently an agreeable feeling of bienaise attending its first impression; but this is also an ordinary consequence of known depressing agencies, as of tobacco, the warm bath, and even bleeding. Often too the pulse and respiration are at first somewhat hurried; but they are more frequently directly reduced from the beginning; and, when the former condition takes place, it is so immediately after the commencement of administration, before the vapour can possibly have entered the system, that it may be justly ascribed, as before suggested, to the nervous agitation of the occasion, and might equally accrue, if atmospheric air were substituted for the chloroform. I do not, however, deny that chloroform may sometimes temporarily excite the circulation; but it is much more reasonable to ascribe the fugitive effect to the sympathetic extension, through the nerves, of the first irritant impression of the vapour, from the mucous surface to the cardiac and pulmonary functions, than to its direct influence on them. Finally, I do not admit the occasional examples of muscular spasms, laughter, turbulence, etc., as in any degree evidences of excitement of the cerebral centres; for similar conditions may result also from an immediately opposite condition; the cerebral functions having this seemingly remarkable singularity, that their irritation and depression are very often attended by the same phenomena, even to convulsions and delirium. The apparent symptoms of excitement, therefore, which occur in exceptional cases, having been explained in conformity with the essentially sedative influence of chloroform upon the nervous centres, we are permitted to allow full weight to those symptoms, much the most frequent, which are obviously the result of depression. Post-mortem examination confirms this view. The brain is in the majority of instances found quite healthy, without congestion, showing that there has been no active irritation in the organ; and, when found congested, it has almost always been but moderately so, and not even in the degree which might have been anticipated, considering the frequency of death from asphyxia, which is characterized by venous congestion of the brain with the other great organs.