The solution of morphia should contain a grain in six drops and be as little acid as possible. In injecting morphia, it should be recollected that ⅙ grain is the usual dose to allay pain, and produce sleep; doses even far smaller often suffice for this purpose, though very much greater quantities can be administered by injection, where long use has rendered the patient tolerant of the drug. Some persons dread the puncture considerably; for them the pain may be entirely prevented by numbing the surface with ether-spray (see page 186) before inserting the syringe, though usually the prick is of so little consequence that any precaution of this kind is unnecessary. The cannula should be thrust completely through the skin into the subcutaneous cellular tissue; if the fluid is injected into the skin itself, inflammation and suppuration of the puncture sometimes ensues. After the cannula is withdrawn, the finger should be placed for a few seconds over the puncture, or much of the fluid will leak out again. When large quantities of solution (one or two syringefuls) are injected the cannula need not always be withdrawn, the nozzle can be unscrewed and the syringe charged again; but more than ten or twelve drops injected into one place generally causes much pain, even where the cellular tissue is very loose. The syringe and cannula should be carefully cleaned, by sending plenty of cold water through them each time they are used, or the cannula will rust and become unfit for use. =Collodion= is much used in drawing the edges of small wounds together, &c. Preston’s plastic collodion, or the flexible collodion of the British Pharmacopœia, 1867, have advantages over the common form by furnishing a tougher pellicle, yielding to the movements of the skin beneath without cracking. Collodion should be kept for use in a small wide-mouthed bottle, with stopper and brush, and when employed should be laid on quickly in a thick mass, so that the crust it leaves shall be of one layer. A tougher crust is obtained if a piece of muslin is soaked in the collodion and then laid on the wound, than if the collodion is used alone. =Vaccination.=—The lymph of the vaccine vesicle, taken between the seventh and tenth days, is preserved for use on lancet-shaped slips of bone 1 inch long, called _points_. These are dipped in the lymph as it exudes from the vesicle, and exposed to the air till dry; they are then wrapped in paper ready for use. When used, the lymph should be moistened, by holding them over a vessel of steaming water a few seconds before inserting them in the wound made to receive the lymph. The points often lose the virus in a few days, and should, if possible, be used the same day they are charged.