3. EFFECTS OF HEAT AS A DISINFECTANT.

If the contagia are simply excessively minute portions of bioplastic particles, in Beale's sense, we may be sure they will be easily killed; a heat far below that of boiling water, and very weak chemical agents, destroy all signs of vitality in animal cells and molecules. We might, therefore, hope much from disinfection. Fungi in water are destroyed by a comparatively low heat; while in dry air Penicillium glaucum is not completely destroyed, according to Pasteur, till 127° C. (= 260° Fahr.), and Oidium aurantiacum dies at about the same temperature. On the contrary, the Bacteroid bodies are often extremely stable. Lex found a temperature of 127° C. or 260° Fahr. insufficient to kill them, and after boiling them for half an hour they still showed vital movements; and in Calvert's experiments a heat of no less than 400° Fahr. (= 204° C.) was required to thoroughly destroy them, and some kinds seem unaffected even by strong acids and caustic alkalies. Bastian has, however, stated' that Bacteria and Vibrios are killed at a much lower temperature; his experiments show that a brief exposure to a temperature of 70° C. (= 158° Fahr.) either killed the germs of Bacteria, or completely deprived them of their powers of multiplication. Sanderson found that Bacteria in water are not developed in fluids heated to 366° Fahr. or even boiled. Disinfection, if Bacteridia are to be destroyed, would be then a matter of much greater difficulty. Tyndall has since pointed out what appears to be, at least, a partial explanation of the above discrepancies. He shows, that whilst prolonged boiling failed to sterilize an infusion, successive heatings for a short time, even below the boilingpoint, were successful. The explanation proposed is, that during the period of latency the spores are in a hard state capable of resisting high temperature, but that just before the period of active germination, they become softened, and therefore amenable to the influence of heat. As, however, spores in various stages may exist in the same fluid, successive heatings are necessary so as to arrest each group at the proper time; but by repeating the heatings sufficiently often an infusion may be sterilized at a point below the boiling-point of water. Important in all ways, this question of the nature of contagia is especially so in a practical sense, viz., that of the easy or difficult destruction of these agents. It does not, however, follow that ordinary putrefactive Bacteria are identical with those which may be supposed to produce disease. It is probable that they are quite different, and that disease Bacteria are more easily destructible by heat at least.

Purification of Clothes and Bedding.-The best plan of doing this is certainly by the agency of heat. Dr. Henry, of Manchester, after showing that vaccine matter lost its power if heated to 140° Fahr. for three hours, proposed to disinfect clothing by dry heat. He disinfected scarlet fever clothing by exposure to 212° Fahr. for one hour; woollen clothing from plague patients, after being heated twenty-four hours from 144° to 167° Fahr., was worn with impunity by fifty-six healthy persons for fourteen days. Heat was largely used to disinfect clothing by the Americans in their civil war, both in the form of dry heat and boiling water. It is believed that the cessation of the plague in Egypt, after St. John's day, was due to the increased heat of the air; but possibly the hygrometric condition of the air may have more to do with this. It has also been surmised

'Proceedings of Royal Society, No. 143, p. 224, March, 1873.
9 Ibid., No. 178, p. 569.

that the yellow fever poison is destroyed by an intense heat. Dr. Shaw has collected the few facts which we know on this subject.'

Disinfecting Chambers, that is, hot-air chambers, into which clothing, linen, and bedding are put, are used. The usual arrangement is a furnace with the smoke-shaft passing under or on one side of a brick chamber, and with a hot-air blast from a shaft running through or under the fire into the chamber itself, or into a passage below it, whence it passes into the chamber through a valve; an exit for the hot air is provided at the top of the chamber; the clothes are suspended in the chamber, at a little distance from the walls.

In other cases the bottom of the chamber is made of iron, and the smoke-flue passes beneath it; the iron becomes red hot, and is covered with sand, to prevent the clothes taking fire. Hot air is then poured into the chamber in the same way. The disadvantage of the hot-air blast is the uncertainty and variation in the amount of heat.

Fraser has devised a good form of stove, in which high temperature and the use of sulphurous acid are combined. The articles are wheeled into the stove in the cart that brings them. Dr. Ransom, of Nottingham, has devised a gas stove, viz., an iron box well covered with non-conducting material; in a channel leading to it a gas-jet burns; by means of a regulator (modified from Kemp's regulator) the heat is kept uniform day and night; the hourly consumption of gas is 9 cubic feet for a small stove, which is sufficient for the hospital at Nottingham.

Steam has been also used; and, at Berlin, a steam disinfecting chamber proposed by Dr. Esse,' is said to work well. This chamber is in the form of two iron cylinders of different diameters, one inside the other, and with walls strong enough to withstand the pressure of the steam; between the two cylinders steam enters from a neighboring boiler, and heats the internal cylinder in which the clothes are suspended; at the top of the cylinder is a brass box which dips a little way down, and is pierced with holes at the bottom, so that the air of the inner cylinder can rise into it; in the box is a thermometer. The outer cylinder is covered with wood, and the top of the cylinder with felt, to economize heat; the steam, when it condenses in space between the cylinders, flows out by means of a valve, which is lifted when the water reaches a certain point in the condenser. The clothes are introduced at the top, the lid of the cylinder being lifted up by a pulley; they are not allowed to touch the cylinder, but are suspended from wooden pegs. In an hour's time the heat can be brought to 90° R. (234.5° Fahr.). Another apparatus has been contrived by Esse for mattresses. It is an iron case with a spiral steam pipe in the centre, which heats with compressed steam (two atmospheres).

A steam cylinder has also been used at the London Fever Hospital, for disinfecting the feathers used as bedding.

The ordinary drying closet in a good laundry will sometimes give heat enough, but not always. A baker's oven can also be used on emergency.

The question of temperature has been much discussed. It is desirable to get as high a temperature as possible so as to insure the destruction of disease poison. On the other hand, the temperature must not be too high, for fear of destroying the fabrics.

Ransom found that fine fabrics began to scorch at 255° to 260° Fahr.

1 Trans. Soc. Science Assoc. for 1864, p. 558.

2 Deutsche Vierteljahrsch. für off. Gesundheitspflege, Band iii., p. 534 (1871).

In some experiments, undertaken at the request of the Director-General, A.M.D.,' the following results were obtained :-Woollen fabrics changed color after six hours' exposure at 212° Fahr., or after two hours at 220° Fahr.; generally length of exposure and elevation of temperature were complementary. Cotton and linen showed signs of change of color after six hours at 212° Fahr., or four hours at 220° Fahr. Professor E. Vallin,* of Val de Grâce, found that a piece of new white flannel was not more discolored after two hours at 230° Fahr. than after one ordinary washing, and that even after three hours a piece already washed showed no change; two hours, however, at 240° Fahr. to 250° Fahr. showed distinct change. Cotton and linen did not change until they had been exposed for two hours to 257° Fahr. The strength of the material was not diminished (as shown by a dynamometer) until after two hours at 300° Fahr. Horse-hair became friable after exposure to heat, but this was chiefly an effect of drying, as it regains its ordinary condition after a short time (Vallin, Lake). In Ransom's stove the heat is arranged to be between 235° and 255° Fahr. After an accident at the Southampton Infirmary, where all the clothes, etc., in the chamber were consumed, a modification was introduced by Dr. Ransom; a chain with a link of fusible metal is set free by the melting of the link as soon as 300° Fahr. are reached; this closes a door, shuts off the gas, and prevents any further rise of heat. In the Liverpool Chambers 280° Fahr. has been registered, and no less than 380° Fahr. in the drying closet over the Cockle stove.

There is no doubt considerable variation in the temperature of different parts of the chamber, and the effects on fabrics vary according as they are placed on or near the floor and sides, or suspended in the centre or upper parts. At the Southampton Infirmary, all bedding and clothing are exposed in the chamber after every occasion of use, the mean temperature being under 230° Fahr., but there is distinct deterioration of fabric, a loss incurred designedly in order to secure complete destruction of disease poison.

As before stated, we have no reason to believe that disease germs will resist a temperature of 220° Fahr., or even 212° Fahr., if completely and thoroughly exposed to it. Even when liquids, such as water or milk, have been infected, no case of disease has ever been traced to the use of such liquids after being boiled. It seems therefore unnecessary to carry the heat to excess, 220° Fahr. being in all likelihood sufficient, or even 212° Fahr. with some length of exposure. In the "Army Medical Regulations' (1878) (655a), exposure to a temperature of not less than 212° Fahr. for at least two hours is ordered.

Soaking and Boiling Clothes.-The boiling of clothes is not generally considered so good as baking, but still is very useful. It is desirable to add some chemical agent to the water, and chloride of lime is frequently used in the proportion of 1 gallon of the strong commercial solution to 20 or 30 gallons of water. Carbolic acid (1 part of pure acid and 2 parts of commercial acid to 100 of water) is also much employed. The German military regulations order the clothes to be laid for twenty-four hours in a solution of sulphate of zinc, in the proportion of 1 part to 120, or of chloride of zinc, in the proportion of 1 part to 240, and then to be washed with soap and water, if the clothes cannot be baked. The routine Dr. Parkes

1 By Dr. F. de Chaumont, Lancet, December 11, 1876.

2 "De la Désinfection par l'Air chaud," Mémoires de la Société de Médecine Pu blique et d'Hygiène Professionnelle, 1877.

followed in the case of a large military hospital during war was to receive all dirty clothes into a large open shed, and to plunge them at once into tubs of cold water with chloride of lime. After twelve to twenty-four hours' soaking, according to their condition, they were put into coppers and boiled, chloride of lime being again added to the water; they were then put into the washing-machine, and then dried and baked in a dry closet, heated to the highest point that could be got, about 200° to 230° Fahr. If lice were very numerous, it was a good plan to bake the clothes before soaking; the lice were mostly killed, but some were only torpid, and were still living, after a temperature of probably 200° Fahr. They could, however, be shaken out of the clothes easily even if not dead.

Fumigating Clothes.-This is best done with sulphur, which may be used in the hot chamber, as in Fraser's oven, or the clothes are suspended in a small close chamber or large vat, and a large quantity of sulphur is set on fire, care being taken that the clothes are not burnt. Hair mattresses must be taken to pieces before fumigation if they be much defiled.'

4. EFFECTS OF CHEMICAL AGENTS.

Although numerous experiments have been made upon this point, yet our knowledge still remains somewhat obscure. A large number of substances have been proposed, and many actually tried, with varying results. One cause of discrepancy has been the somewhat loose way in which the term disinfectant has been employed in cases where the action has been little more than deodorant. Chemical agents may be divided into—(a) those which actually destroy disease poison and minute organisms; (b) those which suspend vitality and propagation; and (c) those which merely deodorize, that is, destroy or mask smell. Even such a division cannot be carried out consistently, and all that we can say is, that some substances act powerfully as destroyers of disease poison and minute life, if used in sufficient quantity and degree of concentration; such substances are also generally deodorants. Other substances do not appear positively to destroy disease poison or minute life, but they certainly suspend its vitality for a time, and we may therefore use this interval of suspension advantageously by getting rid of the infected matter without danger in transit.

A further division of chemical agents might be into gaseous, liquid, and solid, and other divisions might also be suggested. Perhaps the most convenient plan will be to state the objects to be attained, and consider the agents which may be used.

Purification of the Air by Chemical Methods.

The great purifying actions of Nature are diffusion, dilution, transference by winds, oxidation, and the fall of rain. In houses the power of ventilation is the only safe method, but some effect can be produced by chemical agencies in aid of ventilation.

The foreign matters in the air which can be removed by chemical means, are carbon dioxide, hydrogen sulphide, ammonia (usually in the form of ammonium sulphide), and various organic substances, arising in an infinity of ways, some being odorous, others not, and of the physical and chemical nature of which little or nothing is known. Air purifiers are also used to check the growth of fungoid, infusorial, or bacteroid organisms. They are. used in the form of solids or of liquids, which may absorb the substances

1 Army Medical Regulations, 1878, part 5, section v., paras. 644-662.

from the air, or of gases which may pass into the air, and there act on the gases or molecular impurities.

(a) Solid Air Purifiers.-Dried earth, quicklime, charcoal, and calcium and magnesium carbolates (phenates), a mixture of lime and coal-tar, are the most important.

Of these charcoal is the most effectual. It presents an immense surface, and has a very extraordinary power of separating and absorbing gases and vapors from the atmosphere,' and oxidizes rapidly almost every substance capable of it. Its action is not indiscriminate, but elective (A. Smith); when charcoal which has absorbed oxygen is warmed, it gives off CO, (A. Smith), a proof of its great oxidizing power. Exposed to the air in bags or shallow pans, its action is rapid and persistent; its effect is especially marked with sewage gases, and with the organic emanations in disease. It also absorbs hydrogen sulphide. Its power of purifying air from organic emanations is really great, and can be employed in hospital wards with advantage.

Of the different kinds of charcoal, the animal charcoal has the highest reputation, and then peat. But the carbon left in the distillation of Boghead coal has been stated to be even better than animal charcoal. If vegetable charcoal be used, it should be rather finely powdered. The disinfecting qualities of charcoal on air scarcely lessen with time if the charcoal be kept dry. Charcoal filters to be placed before the mouth have been recommended by Stenhouse, and might be useful in cases of very impure air. Dried marly earth is much inferior to charcoal, but still can be employed in the absence of the latter.

Quicklime absorbs CO, and perhaps compounds of sulphur, and has been employed for that purpose.

Calcium and magnesium carbolates have been also used; as they give off carbolic acid, their action is probably chiefly in that way.

(b) Liquid Air Purifiers.-Solutions of potassium permanganate (Condy's red fluid), zinc chloride, and lead nitrate are sometimes used, being either exposed in flat dishes, or cloths are dipped in the solution and exposed to the air. They act only on the air which comes in contact with them, but in that way absorb a good deal of impurity. Condy's fluid, when well exposed to the air, seems to have a good purifying effect, and to lessen the close smell of ill-ventilated rooms, and it absorbs hydrogen sulphide, and so will also solution of nitrate of lead.

(c) Gaseous Air Purifiers.-The evolution of gases into the air is the most powerful means of purifying it independent of ventilation. The principal gases are ozone, chlorine, fumes of iodine and bromine, nitrous, sulphurous, and hydrochloric acid, carbolic acid, tar fumes, acetic acid,

ammonia.

Ozone. It has been proposed to disengage ozone constantly into the air of a room, by heating a platinum wire by a Bunsen cell; by half immersing a stick of phosphorus in tepid water in a wide-mouthed bottle; or by mixing very gradually 3 parts of strong sulphuric acid and 2 parts of permanganate of potassium. This last method is that used by Dr. Fox. The amount of ozone can be measured by the common ozone paper, and the stopper put in if the tint is too deep. It is presumed it will then act as a powerful oxidizing agency, and destroy organic matter, as it certainly removes the putrid effluvia of decomposing blood (Wood and

1 Sennebier, quoted by Chevallier, Traité des Désinfect., p. 146, and A. Smith. Ozone and Antozone, p. 25.