For extraction under nitrous oxide, and also to a great extent under ether, the positions of the patients should differ but little if at all from those already advocated, with this exception, it is advisable not to have the head too far back. Before the administration of the anæsthetic is commenced, any removable artificial teeth that may be in the mouth should be taken out; the operator should decide exactly what he intends to do; at the same time it is well not to attempt too much and to avoid pricking the gum during the examination of any roots that it may be necessary to extract. The prop should be placed on sound firm teeth in such a position that the operator can work without being hindered by it, and a final view of the mouth should be taken. Where several teeth have to be extracted at one sitting, their order of removal should be decided upon before the operation is commenced, and if any particular tooth is causing pain, it should be extracted first. The order of removal should also as far as possible be arranged so that changes of instruments are reduced to a minimum. As a rule, lower teeth should be extracted before upper teeth, because if the latter are removed first, the blood may pass down and so obscure the lower ones. Roots should be removed before whole teeth for the same reason. Each tooth or root must be cleared from the mouth before any attempt is made to remove another except in cases where the gum is thoroughly adherent; under this condition the tooth or root may be left and freed from the gum when the patient has recovered. With teeth which have a liability to slip out from between the blades of the forceps, it is well as a precaution to keep a finger of the left hand behind the blades to prevent the tooth passing backwards should it slip out. LOCAL ANÆSTHETICS. (_a_) =Cocaine.=--The most efficacious of the local anæsthetics in use is cocaine. It is an alkaloid obtained from the dry leaves of Erythroxylon Coca, and in practice the hydrochlorate form is generally used. For the removal of teeth it is necessary to inject a solution of the drug into the tissues, a simple application to the gum being of little use. Cocaine has the reputation of not being thoroughly reliable in its action, but this in a great measure often arises from want of care in injecting it. Not more than half a grain should be injected for the removal of a tooth, and even then with people of feeble health, untoward symptoms may supervene.