More common than gases and most readily suggested as disinfectants are certain liquids which have been proved both by laboratory experimentation and by actual experience to have the power of killing bacteria when brought into contact with them. Those liquids which have commended themselves particularly have additional advantages in not destroying fabrics, metals, or tissue with which they are brought in contact and in being purchasable at moderate prices. There is little choice between a number of such liquids, and the number of modifications or combinations which are made and bottled and sold under some fancy name is legion. But the label, the name, and the additional price add nothing to the value of the basic chemical from which they are all compounded, and except for their convenience, they have little to recommend them. _Carbolic acid as disinfectant._ Carbolic acid is one of the most useful of these liquids, and in its various forms appears in almost all disinfectants. It may be obtained from the drug store in two forms, either as a crystal or as a concentrated solution. A 2 per cent solution, that is, one pint of carbolic acid to six gallons of water, is the proper strength for all such uses as wiping off wooden surfaces, furniture, floors, etc. A stronger (5 per cent) solution is used when it is intended to destroy organic matter containing large quantities of germs. This is practically a saturated solution, so that if a bottle be partly filled with the crystals of carbolic acid and then completely filled with water, the water will absorb enough of the carbolic acid to make a 5 per cent solution, and the water may be poured on and off as long as the crystals remain. This 5 per cent solution is the proper strength to receive sputum from tuberculous patients, material ejected from the stomach in diphtheria, and fecal matter from typhoid and cholera patients. This strong solution should not be used on the living human body, since it is powerful enough to eat directly into the flesh, and being a violent poison, it should be kept out of the way of the household and carefully labeled to avoid accidents. Carbolic acid has no value at all in the way of disinfecting the air, although fifty years ago surgeons were accustomed to use a spray of carbolic acid around the operating table before an operation in order to destroy any germs of the air lingering in the vicinity. It is equally futile to pour carbolic acid into sewers or to stand it around on the mantelpiece for the purpose of disinfecting a room. Nor are sheets wet in carbolic acid and hung over doorways and at the end of passages anything more than a remnant of medievalism. _Coal-tar products._