DISINFECTANT 37 



acts partly in conjunction with the soil and the rain to cause disinfection, and partly 

 by its own power, it also acts mechanically as a means of removing all noxious 

 vapours. The wind and other currents of the air are continually ventilating the 

 ground, and when these movements are not sufficiently rapid, or when they are inter- 

 rupted by our mode of building, we are compelled to cause them artificially, and thus 

 we arrive at the art of ventilation. The addition of one-tenth per cent, of car- 

 bonic acid to the air may be perceived, at least if accompanied with the amount 

 of organic matter usually given out at the same time in the breath, and as we exhale 

 in a day 12-16 cubic feet of that gas, we can injure the quality of 16,000 cubic 

 feet of air in that time. The great value of a constant change of air is therefore 

 readily proved, and the instinctive love which we have of fresh air is a sufficient 

 corroboration. 



Cold is a great natural disinfectant. The flesh of animals may be preserved as far 

 as we know for thousands of years in ice ; putrefying emanations are completely 

 arrested by freezing, but the mobility of the particles, or chemical action, is also 

 retarded by a degree of cold much less than freezing, and beginning at 54 Fahr. 



Heat is also a disinfectant, when it rises to about 140 of Fahrenheit, according to 

 Dr. Henry. But as a means of producing dryness it is a disinfectant at various 

 temperatures. Nothing which is perfectly dry can undergo putrefaction. On the 

 other hand heat with moisture below 140 is a condition very highly productive of 

 decomposition and all its resulting evils. Disinfection by heat is used at quarantine 

 stations. Light is undoubtedly a great disinfectant ; so far as we know, it acts by 

 hastening chemical decomposition. In all cases of ventilation, it is essential to allow 

 the rays of light to enter as well as the currents of air. Its effect on the vitality of 

 the human being is abundantly proved, and is continually asserting itself in vege- 

 tation. The true disinfecting property of light exists in all probability in the 

 chemical rays which cause compositions and decompositions. Water is scarcely to bo 

 called a disinfectant itself except indirectly, for it increases putrefaction, but as a 

 mechanical agent of purity the most remarkable, and there is no other capable of 

 taking its place actively. "Wherever animals, even human beings, live, there are 

 emanations of organic matter, even from the purest. The whole surface of the house, 

 furniture, floor, and walls, becomes coated by degrees with a thin covering, and this 

 gradually decomposes, and gives off unpleasant vapours. Sometimes it becomes 

 planted with fungi, and so feeds plants of this kind. But long before this occurs a 

 small amount of vapour is given off sufficiently disagreeable to affect the senses, and 

 sometimes affecting the spirits and the health before the senses distinctly perceive it. 

 This must be removed. In most cases this film is removed by water, and we have 

 the ordinary result of household cleanliness ; but in other cases when the furniture is 

 such as will be injured by water, the removal is made by friction or by oil or turpen- 

 tine, and other substances used to polish. Water as a disinfectant is used also in 

 washing of clothes ; for this purpose nothing whatever can supply its place, although 

 it requires the assistance both of soap and friction, or agitation and heat. Water is 

 also used as a mechanical agent for removing filth generally, and the method which 

 Hercules devised of using a river to wash away filth is now adopted in all the most 

 advanced plans of cleansing towns. It is only by means of water that the refuse of 

 towns can be conveyed away in covered and impervious passages, whilst none what- 

 ever is allowed to remain in the town itself. In cases where this cannot be done, it 

 is much to be desired that some disinfecting agent should be used to prevent decom- 

 position. Where water is not used, as in water-closets, there is generally a great 

 amount of matter stored up in middens, and the town is of course continually exposed 

 to the effluvia. Beside these methods of acting, water disinfects partly by preventing 

 effluvia from arising from bodies, simply because it keeps them in solution. This 

 action is qot a perfect one, but one of great value. The water gives off the impurity 

 slowly, sometimes so slowly as to be of no injury, or it keeps it so long that complete 

 oxidation takes place. The oxygen for this purpose is supplied by the air, which the 

 water absorbs without ceasing. To act in this way, water must be delivered in 

 abundance. Bodies decompose rapidly tinder water, and it acts also as a great 

 opponent to disinfection by rising up in vapour loaded with the products of decom- 

 position. 



Mere drying is known to arrest decay, as the mobility of the particles in decompo- 

 sition is stayed by the want of water. We are told in Andersson's Travels in S. Africa, 

 that the Damaras cut their meat into strips, and dry it in the sun, by which means it 

 is preserved fresh. A similar custom is found in S. America. Certain days prevent 

 this, and decomposition sets in rapidly. A little overclouding of the sky, or a little 

 more moisture in the air, quickly stops the process. 



The above may be called natural disinfectants, or imitations of natural processes, 

 charcoal being introduced as an example of a more decided character of porous action. 



