(1) One danger is that just mentioned, of paralysis of the respiration from an overdose. This, however, is one of the least of the dangers, and if the enfeeble-ment of the respiration be observed in time, it is generally possible to save the patient by stopping inhalation, and keeping up artificial respiration for a little while if necessary.

(2) Another danger is from paralysis of the heart by a too concentrated chloroform vapour. This is indicated by a sudden stoppage of the heart, paleness of the face, and dilatation of the pupil while the respiration may continue.

If this accident should occur, the body of the patient should be inclined so that the head should be lower than the feet, and artificial respiration should be kept up briskly but regularly, the expiratory movements being made by pressure on the thorax and especially over the cardiac region, so that the mechanical pressure should stimulate the heart, if possible, to renewed action. The vapour of nitrite of amyl may also be administered by holding a piece of blotting-paper or cloth on which a few drops have been sprinkled before the nose, while artificial respiration is kept up.

The inspiratory movements may be made by drawing the arms backwards over the head, as in Sylvester's plan.

(3) A third danger arises from stoppage of the heart by a combination of chloroform-narcosis and shock. This is one of the most dangerous conditions. It may occur even during full chloroform-narcosis in animals from operations on the stomach; but it is much more common in men from imperfect anaesthesia. In very many cases of so-called death from chloroform during operations, we find it noted as a matter of surprise that death should have occurred as the quantity of chloroform given was so small. The reason that death occurred probably was because the quantity of chloroform given was so small. Had the patient been completely anaesthetised, the risk would have been very much less. The reason why imperfect anaesthesia is so dangerous is, that chloroform does not paralyse all the reflexes at the same time. A very large proportion of the deaths from chloroform occur during the extraction of teeth, and we may take this operation as a typical one in regard to the mode of action, both of the sensory irritation and of the chloroform. When a tooth is extracted in a waking person, the irritation of the sensory nerve produced by the operation has two effects : - 1st, it may, acting reflexly through the vagus, cause stoppage of the heart and a consequent tendency to syncope. 2nd, it causes reflex contraction of the arterioles, which tends to raise the blood-pressure and counteract any tendency to syncope which the action of the vagus might have produced.

In complete anaesthesia all these reflexes- are paralysed, and thus irritation of the sensory nerves by the extraction of the teeth has no effect either upon the vagus or upon the arterioles. In imperfect anaesthesia, however, the reflex centre for the arterioles may be paralysed (vide p. 204), while the vagus centre is still unaffected. The irritation caused by the extraction of the tooth may then cause stoppage of the heart, and there being nothing to counteract the tendency to faint, syncope occurs and may prove fatal.

With nitrous oxide there is very much less danger, inasmuch as the nitrous oxide causes a venous condition of the blood, with consequent contraction of the arterioles and rise in the blood-pressure, so that any tendency to syncope through vagus-irritation is efficiently counteracted.

With ether, also, the danger is very much less, probably because it has a more equal effect on the centres (vide p. 204).

(4) Another danger is that of suffocation from blood passing into the trachea in operations about the mouth or nose, or from the contents of the stomach being drawn into the larynx when vomiting has occurred during partial anaesthesia. In consequence of this, it is better, instead of giving chloroform or ether during the whole of an operation on the mouth or nose, to give it only at the commencement, and to administer along with it, or before it, a hypodermic injection of one-sixth to one-third of a grain of morphine. The chloroform anaesthesia thus passes into the morphine narcosis, and the operation can be finished without pain, and without danger.

To prevent the occurrence of vomiting, it is advisable not to give solid food for some hours before an operation, though if necessary a little beef-tea or stimulant may be given half an hour or so before the administration of the anaesthetic.