Downy and fibrous materials readily receive infection; it may, in fact, in many instances, be folded up in them, and so retained almost any length of time; but if they are thoroughly exposed to a free current of air, it is dissipated in a short time. It should be mentioned, that infectious diseases are more readily received in certain states of the body; thus, fear, timidity, mental anxiety, and such states of mind, by lowering the general tone of the system, render it much more liable to contract infectious or contagious diseases; a state of exhaustion from bodily fatigue, or from hunger, has the same tendency. Infection is also more readily received through the lungs than through the skin; therefore, it is important never to receive the breath of a patient, and, as a sailor would say, always to keep to the windward side of him. Amongst the domestic disinfectants, vinegar has a great reputation, but undeservedly so; its only action is to overpower, by its odor, the smell of a sick room - as a destroyer of the peculiar influences that engender disease, it has no power. Burning substances act in the same manner. Burnt brown paper, fumigating pastiles, tobacco, only act by substituting one smell for another. The ridiculous practice of carrying about a piece of camphor is very common, and is perfectly inefficacious. If it has any action at all, it must be an injurious one; for camphor is a stimulant, and its constant inhalation must tend to lower the system, and so produce the very evil it is supposed to remedy.

The best means of preventing infection, are ventilation and cleanliness in every particular. The best means of destroying it are those powerful chemical agents which have the power of uniting with the hydrogen which is supposed to form part of the infectious substances.

The most powerful, easily controlled, and in every sense the best disinfectant, is chlorine gas. This agent at once destroys every trace of infection in all substances submitted to its action. Its formation is perfectly under control, and goes on in a gentle manner for days together, without requiring care or attendance. We consider that the slow liberation of chlorine is far superior to the employment of chloride of lime, which gives forth the gas in a modified form.

In one case of a school where scarlet-fever had returned after several attempts at purification, chlorine effected the complete removal of every trace of the disease. Various modes of liberating chlorine are known to chemists; but, for such purposes as the present, where a slow, uniform, and constant action is required, there are none equal to the following plan:- One pound of common table-salt is to be intimately mixed by stirring with an equal weight of a substance called manganese, which may be readily obtained from any good chemist. Small portions of this mixture should be placed in shallow pans (the saucers of common flower-pots answer the purpose); and upon them should be poured a mixture of oil of vitriol (sulphuric acid) and water, the quantity required for the above weights, viz., for one pound of each in-gredient, being two pounds of oil of vitriol and one of water, both by weight. These should have been previously mixed in a wooden vessel, being stirred by a wooden lath, and allowed to become cool before being poured on the salt and manganese.

as the mixing of the acid and water generates great heat. Too much care cannot be taken with the acid, as it is excessively corrosive in its nature, and destroys most substances with which it comes in contact. When these materials are all mixed, chlorine is slowly evolved for a period of three or four days, and in so gentle a manner, that not the slightest irritating or unpleasant effect is produced. If it is wished to cause the more rapid production of gas, the saucer may be placed over a basin of boiling water, or upon a hot brick; but the slow generation for a considerable length of time is what should be more especially aimed at. It is needless to say, that all substances supposed to have been contaminated, should be spread out so as to receive the influence of the gas; the bed-linen, and all woollen garments, being exposed by being spread out on chairs, lines, etc.; the drawers and cupboards opened; and while the disinfecting is in actual operation, the windows and doors should be kept shut, to prevent the dissipation of the chlorine. It is found that two ounces of manganese, with a. proportionate quantity of the other materials, is sufficient for a room twenty feet wide, forty feet long, and twelve feet high, which contains 20 X40xl2=9600 cubic feet.

It may be mentioned, that breathing chlorine in this highly diluted state, is not injurious to the general health; although, in a concentrated form, or unless very much diluted with air, it is irritating in the highest degree. In the very dilute state, it is occasionally prescribed for the inhalation of consumptive patients.

For the satisfaction of those who rely on the authority of a great name, it may be stated, that chlorine used in the manner here recommended, was employed by one of the most illustrious of English chemists, in the case of the Penitentiary, when a violent and fatal disease broke out there, and with complete success. The operator in this case was Faraday. It may occasionally be found more convenient to use another mixture for the liberation of chlorine gas, in which case the following may be employed:__

One part of manganese is to be drenched with four parts by weight of muriatic acid (spirits of salts), mixed with one part of water. The gas is evolved slowly in the cold, and rapidly if assisted by a gentle heat. This process is rather more expensive, and possesses no advantage over the one previously described.