This same method is sometimes applied in dealing with certain abnormal fermentations that are apt to occur on the farm. It is particularly useful with those tainted milks known as "sweet curdling." The ferment organisms concerned in this change are unable to develop in the presence of lactic acid bacteria, so the addition of a clean sour milk as a starter restores the normal conditions by giving the ordinary milk bacteria the ascendency.
Chemical disinfection. In exceptional instances it may be necessary to employ chemical disinfectants to restore the normal conditions. Of course with such diseases as tuberculosis, very stringent measures are required, as they are such a direct menace to human life, but with these abnormal or taint-producing fermentations, care and cleanliness, well directed, will usually overcome the trouble.
If it becomes necessary to employ chemical substances as disinfecting agents, their use should always be preceded by a thorough cleansing with hot water so that the germicide may come in direct contact with the surface to be disinfected.
It must be borne in mind that many chemicals act as deodorants, i.e., destroy the offensive odor, without destroying the cause of the trouble.
Sulfur is often recommended as a disinfecting agent, but its use should be carefully controlled, otherwise the vapors have but little germicidal power. The common practice of burning a small quantity in a room or any closed space for a few moments has little or no effect upon germ life. The effect of sulfur vapor (SO2) alone upon germ life is relatively slight, but if this gas is produced in the presence of moisture, sulfurous acid (H2SO3) is formed, which is much more efficient. To use this agent effectively, it must be burned in large quantities in a moist atmosphere (three lbs. to every 1,000 cubic feet of space), for at least twelve hours. After this operation, the space should be thoroughly aired.
Formalin, a watery solution of a gas known as formaldehyde, is a new disinfectant that recent experience has demonstrated to be very useful. It may be used as a gas where rooms are to be disinfected, or applied as a liquid where desired. It is much more powerful in its action than sulfur, and it has a great advantage over mercury and other strong disinfectants, as it is not so poisonous to man as it is to the lower forms of life.
Bleaching powder or chloride of lime is often recommended where a chemical can be advantageously used. This substance is a good disinfectant as well as a deodorant, and if applied as a wash, in the proportion of four to six ounces of the powder to one gallon of water, it will destroy most forms of life. In many cases this agent is inapplicable on account of its odor.
Corrosive sublimate (HgCl2) for most purposes is a good disinfectant, but it is such an intense poison that its use is dangerous in places that are at all accessible to stock.
For the disinfection of walls in stables and barns, common thin white wash Ca(OH)2 is admirably adapted if made from freshly-burned quick lime. It possesses strong germicidal powers, increases the amount of light in the barn, is a good absorbent of odors, and is exceedingly cheap.
Carbolic acid, creosote, and such products, while excellent disinfectants, cannot well be used on account of their odor, especially in factories.