CHAPTER XLVII.

DISINFECTION.

By disinfection is meant the destruction of the active cause of each infectious disease. A disinfectant is therefore synonymous with a _germicide_. Disinfectants must be distinguished from _deodorants_ or deodorisers, such as charcoal, and from _antiseptics_, which are antagonistic to the growth of bacteria, without necessarily killing them, _e.g._ common salt. Disinfection may be effected by chemical or physical means.

CHEMICAL DISINFECTANTS.

A chemical disinfectant should fulfil the following conditions: 1. It must be an efficient germicide. 2. Its germicidal power should not be destroyed by the fæcal or other polluting matter, with which the bacteria of infection are associated. 3. For many purposes, it must not be destructive to or liable to stain the skin, or fabrics, or other articles to which it is applied. 4. It should preferably not be a virulent poison; and should be moderately cheap. The search for a completely non-poisonous disinfectant is a chimera.

There are three great =classes of chemical disinfectants=.

1. Oxidising agents, as the halogens (chlorine, etc.) and permanganates.

2. Deoxidising agents, as sulphurous acid (SO₂) and formic aldehyde (CH₂O).

3. Other disinfectants, which act by coagulating protoplasm or otherwise, as carbolic acid, corrosive sublimate.

The number of disinfectants is legion. Only the chief ones can be mentioned and their chief properties described. It is a good rule to eschew the use of all disinfectants of which the exact composition is not given; and all disinfectants which are described by “fancy” names, which are not descriptive of their composition.

A. OXIDISING AGENTS.

=Chlorine= has been most commonly used as chloride of lime (CaCl₂, Ca(ClO)₂). This is somewhat unstable in composition. A solution of sodium hypochlorite containing 10 per cent. of available chloride is preferable. Chloride of lime for sprinkling on decomposing matter should contain at least 10 to 15 per cent. of available chlorine. Sulphuretted hydrogen and other offensive gases are decomposed by it. Thus

SH₂ + Cl₂ = S + 2HCl. Its chief action is as an oxidising agent. Thus H₂O + Cl₂ = 2HCl + O.

A large excess must be used in disinfecting, otherwise the chlorine may simply oxidise fœcal or other organic matter, and not effectually destroy contagia.

_Methods of Use_—(_a_) As a gas, by the action of hydrochloric acid on strong chloride of lime. The molecular density of chlorine is 35·5, of formic aldehyde 15, of sulphurous acid 32; and the rate of diffusion of gases being inversely to the square-root of their densities, clearly chlorine does not compare favourably as a gas with formic aldehyde. The bleaching effect of chlorine on coloured articles of apparel is a disadvantage.

(_b_) As a liquid: used thus chlorine is very efficient, applied either as a spray or brushed on walls and other surfaces. Delépine found that a solution of one part of chloride of lime in 100 parts of water applied to wall paper impregnated with tubercular matter, disinfected it in a few hours, or in a few minutes if the layer of infected matter was not thick.

=Bromine=, =Iodine=, and =Euchlorine= (a mixture of chlorine and Cl₂O₄) are efficient disinfectants.

=Iodine Trichloride= (ICl₃) was found by Behring to share with corrosive sublimate (HgCl₂) carbolic acid and cresol mixed with acids (see page 327), the halogens (Cl, Br, and I), and chloride of lime a superiority over other disinfectants in their power of killing anthrax spores in a short time.

=Permanganates= have been largely used as disinfectants, but their value is small. Impure sodium manganate (Na₂MnO₄) with much common salt (NaCl) containing some permanganate is known as “Condy’s Green Fluid.” “Condy’s Red Fluid” consists of permanganate and sulphate of soda. To be of any use it must be employed in 5 per cent. solution. It stains fabrics brown, and it exhausts its feeble disinfecting power in first oxidising decomposing organic matter.

B. DEOXIDISING AGENTS.

=Sulphurous Acid= (SO₂) acts chiefly as a reducing agent on organic matter. It is used chiefly as a gaseous disinfectant, and for this purpose is generated (_a_) by burning 1 lb. of sulphur for every 1,000 cubic feet of space in the room (which will equal 1·12 per cent. of SO₂). The windows and chimney of the room are first closed; the sulphur is placed in a saucepan supported over a bucket of water, and its ignition is aided by a small quantity of methylated spirit. The door of the room is then sealed, and the room left until the next morning. (_b_) Carbon disulphide may be burned in a benzoline lamp. (_c_) SO₂ liquefied under pressure is supplied in cylinders available for convenient use. The experimental results of the action of SO₂ on various bacteria are somewhat discrepant. It probably is fairly efficient for some diseases, but not in tuberculosis.

=Formaldehyde= or Formic Aldehyde (CH₂O) is produced by the slow and incomplete oxidation of methyl alcohol (CH₃OH) under access of air. A saturated solution in water containing 40 per cent. of the formaldehyde gas is known as =formalin=. The simple evaporation or heating of formalin is liable to produce the polymeric _paraform_ which is solid and inert. To prevent the formation of paraform when formalin is evaporated, Trillat adds to it a solution of calcium chloride (C_a_C_l_₂), the mixture being known as _formochloral_. It is stated that when the air of a room is charged with less than one per cent. of the vapour, rapid and complete disinfection of surfaces occurs, and that it possesses a certain amount of penetrating power into loose fabrics. No damage is done to textile fabrics; and disinfection by this means possesses the advantage over disinfection by sulphurous acid or chlorine that the room can be entered without serious discomfort soon after the disinfection is carried out. In solution formalin is undoubtedly a powerful disinfectant, and in the gaseous condition it is at least equal in value to SO₂, probably better. Formaldehyde is used as a disinfectant.

(_a_) By evaporating a 60 per cent. solution of CH₂O in methyl alcohol (trade name _holzine_) over pieces of glowing coke placed under an asbestos plate (Opperman-Rosenberg apparatus). (_b_) By subliming tabloids of paraform by the heat of a lamp. A methylated spirit lamp is employed, and the moisture from the combustion in this causes the transformation of a considerable proportion of paraform into CH₂O vapour. It is doubtful if the quantity of the latter evolved is sufficient for efficiency. (_c_) In Trillat’s apparatus formalin (_i.e._ the 40 per cent. solution in water of CH₂O) with CaCl₂ solution is heated in an autoclave worked at a pressure of 40 lbs., provided with a pressure gauge and thermometer. In all these methods the room must be carefully sealed, as the tendency for the disinfectant to escape is greater than with SO₂ or C_l_. (_d_) The best method is to spray a solution of formalin 4 oz. to one gallon of water on all the surfaces of the room (see page 333). This is equal to a strength of 1 in 40 of formalin, or 1 in 100 of formic aldehyde.

C. OTHER DISINFECTANTS.

TAR ACIDS.—When coal tar is treated by acids and alkalies in succession, it becomes separated into (1) hydrocarbons, (2) phenols or tar acids, carbolic, cresylic, etc., (3) aniline and other basic substances. The hydrocarbons are known in commerce as “neutral tar oils.” They are brown and syrupy, turning milky with water, and feebly disinfectant. The two most important “tar acids” are phenol or carbolic acid (C₆H₅OH) and methyl-phenol, also called cresol or cresylic acid (C₆H₄(CH₃)OH). The higher members of this same group yield milky emulsions with water, and are less poisonous than phenol. Various mixtures of them are used as disinfectants, and sold as creolin, Jeye’s and Lawes’ fluids. Izal belongs to the same series.

=Carbolic Acid= (phenol) did not kill anthrax spores until a 3 per cent. strength of its solution was used for 7 days (Koch), but sporeless anthrax bacilli were destroyed in a few minutes by a 1 to 2 per cent. solution. The disinfecting power of carbolic acid is greatly increased by adding mineral acids. Carbolic acid and lysol are superior to creolin for disinfecting stools. A 5 per cent. solution of carbolic acid destroys tubercle bacilli in sputum in 24 hours. _Carbolic acid powders_ are in common use. In my opinion quicklime is more valuable.

=Cresol= is obtained from “crude carbolic acid” by fractional distillation at a temperature between 185° and 205° C. A one-half per cent. solution has equal disinfecting power to a 2 or 3 or sometimes a 5 per cent. of phenol (carbolic acid).

=Creolin= consists of cresol emulsified in a solution of hard soap. Behring classifies the comparative germicidal power of phenol, cresol, and creolin on bacteria in broth as 1, 4, and 10 respectively. When albumen is present, creolin loses a part of its disinfectant power.

=Lysol= contains 50 per cent. of cresol, dissolved by means of neutral potash soap. It is completely soluble in water and does not turn milky as creolin does when water is added. It is more effective than creolin, and still more than HgCl₂ in albuminous liquids.

=Soap= has, owing to its alkalinity, disinfectant as well as cleansing action. A temperature of 55°-75° C. greatly aids its action. _Antiseptic soaps_ possess no special value as germicides, but carbolic soap is a useful insecticide.

=Lime= in a one-tenth per cent. solution destroys typhoid and cholera microbes.

=Mercuric Chloride= (HgCl₂, corrosive sublimate) was found by Koch to destroy anthrax bacilli in a dilution of 1 in 20,000. Others have obtained less favourable results, but it is certainly a powerful germicide. The germicidal effect is greatly diminished by contact with organic matter, an insoluble albuminate of mercury being produced. For this reason HgCl₂ is not the best disinfectant for fæces unless mixed with acid, as in the following solution: HgCl₂ ½ oz., HCl 1 oz., aniline blue 5 grains to three gallons of water. This gives a solution of 1 in 960. The colouring is added to avoid accidental poisoning. HgCl₂ is not a good disinfectant for linen. Stains are apt to be fixed by it, and if linen soaked in it is subsequently washed with soap, without first carefully washing out the HgCl₂, it is darkened in colour. It attacks metals, and must not therefore be placed in metal receptacles.

=Chloride of Zinc= in a solution containing 25 grains to the fluid drachm is known as “Sir William Burnett’s solution.” It is a good deodorant, but an inefficient disinfectant.

=Chinosol= (C₉H₆NKSO₄) belongs to the quinoline group. It is an almost inodorous powder, very soluble in water, noncorrosive, and does not stain. A solution of 1 in 1200 forms an efficient germicide.

DISINFECTION BY PHYSICAL MEANS.

Natural processes tend to the destruction of pathogenic microbes after their elimination from the patient. Of these desiccation, sunlight, and fresh air are the most potent. Heat and cold have a similar effect. Filtration or mechanical separation deprives a contaminated liquid of its microbes.

=Desiccation= attenuates the virulence of and finally kills most microbes. In laboratory experiments the vibrio of Asiatic cholera when dried dies in from three hours to two days, according to the degree of desiccation. The bacilli of enteric fever, tuberculosis, and diphtheria only die after drying for a few weeks or even months. The anthrax bacillus may retain its vitality for several years in a desiccated state. Clearly, therefore, desiccation has no administrative value in the prevention of disease, and on the contrary it aids the dissemination of the microbes of tuberculosis, small-pox, scarlet fever, etc.

=Direct Sunlight= kills a large proportion of the sporeless pathogenic microbes. Diffuse is less energetic in its action than direct sunlight. The bacillus of diphtheria is destroyed by a half to one hour’s exposure to sunlight. As to tubercle bacilli, see page 316. Downes and Blunt showed that diffused sunlight retards the putrefaction of organic infusions, and that direct sunlight inhibits putrefaction. Sunlight cannot, however, be trusted as an efficient disinfectant. It only secures _surface_ disinfection, and could not be relied upon for pillows, mattresses, etc. M. Ward’s experiments showed that the actinic rays of the sun are germicidal, independent of the heat.

=Fresh Air=, like sunlight, should be employed as a valuable auxiliary, not as an agent to be depended upon apart from systematic disinfection. The experiments of Downes and Blunt showed that light and oxygen together accomplished what neither alone could do. The presence of air in anthrax increases danger. The anthrax bacillus does not form spores in an animal suffering from this disease, and does not do so _post mortem_, unless the animal is dissected. Hence the importance of keeping the skin unbroken in this disease, only examining a drop of blood to establish the diagnosis.

=Filtration= is a means of separating microbes from the gases or liquids containing them. For the filtration of water see page 96. The carbolic sheet outside a sick-room is supposed to filter the air leaving the room from microbes. It is probably useless except as a reminder to the nurse to change her dress and adopt other precautions on leaving the sick-room.

=Settlement of dust= also acts as an aerial disinfectant. If a room be locked up, its air next day is almost free from particles, and all that is then required is _disinfection of the surfaces_ of the room and of the articles in it. Whatever method of disinfection is employed, it is not disinfection of the air, but of the surfaces of a room which is the end in view.

=Washing= is the most efficacious means of removing infection. It is a mechanical means of removing the particular matter of which the contagium consists from the person or article to which it adheres into the water, which subsequently enters the drain, in the same way as do urine and fæces. Washing is an absolutely efficient means of purifying articles that can be completely submitted to it. A consideration of the =physical laws governing the spread of infection= will make this clear. The contagia are passive. When contained in a liquid they cannot escape from it under ordinary circumstances. Thus foul smelling gases may escape from sewage, but bacteria do not escape, except rarely during bubbling, or from dried portions of the invert of the sewer. Barring rare accidents “microbes submerged are imprisoned.” Contagia are harmless until they become dust. Hence the danger associated with the use of pocket handkerchiefs in such diseases as influenza and phthisis; and the importance of keeping all infectious discharges wet, until they can be finally disposed of.

DISINFECTION BY HEAT.

Heat may be applied in various ways: (1) Prolonged boiling in water of materials which are not spoilt by this means. (2) Destruction by fire of infected articles. (3) Dry hot air. (4) Steam.

=Boiling= kills most pathogenic microbes. The cholera vibrio is killed in four minutes at a temperature of 52° C. (126° F.); the typhoid bacillus at 59°.4 C. (138°.8 F.) in ten minutes. If boiling be continued for five minutes, the spores of pathogenic microbes are killed. The addition of one to two per cent. of washing soda to the water hastens this effect. For infected linen nothing beyond this is required.

=Destruction by Fire= is to be recommended for comparatively worthless articles, such as toys, straw from beds, rags, old clothing and bedding.

=Dry Hot Air= has been largely used in the past in ovens, for the disinfection of bulky bedding. It is now entirely superseded by steam. Its disadvantages are that (_a_) heat penetrates very slowly into the interior of bedding. Disinfection in test experiments was not accomplished in the interior of small bundles of clothes in three or four hours. (_b_) Scorching of articles often occurs. The sole advantage of this method is that bound books and leather goods are less liable to be damaged by it than by steam. If no other apparatus is available a baker’s oven will serve to kill the non-sporiferous microbes of cholera, enteric fever, and diphtheria, as well as animal vermin. If, however, we accept the proper test proposed by Buchanan of the efficacy of disinfection, the “destruction of the most stable known infective matter,” dry heat is unsatisfactory.

=Steam= may be employed as a disinfectant either (_a_) _superheated_, or (_b_) _saturated_, _i.e._ close to the temperature at which condensation occurs. This temperature depends upon the pressure under which the water has been boiled. At ordinary atmospheric pressure it is 100° C. (212° F.). The temperature of boiling is raised by subjecting the water to pressure. Consequently boiling water and the steam produced from it may be at any temperature. Thus steam may be

(_a_) Under pressure, with a temperature above 212° F. (_b_) Not under pressure, at a temperature of 212° F.

Steam when admitted into a disinfecting stove comes into contact with cold objects. _If the steam is saturated_, immediate condensation to 1∕1600 part of its original volume occurs. Its latent heat is at the same time evolved. The condensation causes enormous shrinkage in bulk. More steam is thus insucked into the partial vacuum produced, and this is repeated, until in every part of the mattress or other material undergoing disinfection equality of temperature is reached, when condensation of steam will cease, and disinfection is complete. _If the steam is superheated_ and no condensation allowed, disinfection occurs by the relatively slow method occurring with dry heat. In practice at the early stage cooling causes some conversion of superheated into saturated steam, though subsequently the much slower process of disinfection by conduction of heat goes on. Hence superheated steam is a less efficient disinfecting agent than saturated steam.

Superheating is produced in disinfecting stores in two ways: (1) By a jacket around the stove, which is kept at about double the pressure and about 20° to 30° F. hotter than the interior of the stove; as in the older patterns of the Washington Lyon stove. (2) By having a jacket containing a solution of calcium chloride, which is heated by a furnace under the stove. This solution is kept at a constant strength by an automatic supply from a cistern. The temperature of the boiling water is thus raised without pressure to 225° F. This is the principle of Thresh’s stove. The object of superheating steam is to assist in rapidly drying materials; but this object can equally well be secured by periodically allowing the sudden escape of the steam confined under pressure, in pressure disinfectors. This last method is the best, as it can not only be utilised at the last stage of the disinfection for drying the articles; but at the earlier stage for sweeping the air out of the stove, and thus removing what, owing to its low conductivity for heat is one of the most serious obstacles to rapid and efficient disinfection.

In the above description it has been assumed that the steam, whether saturated or superheated, is =confined=, except when the exhaust is employed for drying purposes. Steam may also be employed as =current steam=. Current steam disinfectors are initially cheap, but more steam, and therefore more fuel, is required in their use; and unless pressure is used by impeding the escape of the steam a temperature of only 212° F. can be secured. Accepting Buchanan’s dictum, a stove supplying saturated steam under pressure at a temperature in the interior of the stove of 234° F. is to be preferred. This temperature with saturated steam destroys the spores of the most resistant known microbe (that of symptomatic anthrax). With superheated steam or hot air stoves on the same basis a temperature of 280° F. would be required, which is damaging to most textiles, except horsehair.

THE PRACTICE OF DISINFECTION.

The =Management of the Sick-room and Patient= requires careful and conscientious attention to detail. Certain details are given on page 319. All unnecessary furniture, carpets, and hangings should be removed as soon as the nature of the illness is known; but unless these articles have been contained in close trunks or drawers, and not opened since before the onset of the illness, they must be disinfected. Food left over from the patient’s meals must be burnt, if solid, in the patient’s room; if liquid, emptied down the water-closet. Dry sweeping of the floors is to be avoided, only wet brushing or cloths being used. Volatile aerial disinfectants during the sickness are valueless.

The =Treatment of Discharges from the Patient= is the most important point in the management of infection. The stools should be received into a bed-pan containing a 5 per cent. solution of carbolic acid, a 3 per cent. solution of cresol or lysol, or a 5 per cent. solution of chloride of lime. Milk of lime (20 per cent. strength) is very reliable, when added like the preceding solutions in bulk equal to that of the stool to be disinfected. The urine and vomit, if any, should be treated in exactly the same way. The infection of enteric fever is often spread by undisinfected urine.

Discharges from the =throat, nose and mouth= of patients should be received into a solution of

lysol 5 oz. to 1 gallon of water, or carbolic acid 7 oz. „ „ „

The efficacy of the carbolic acid solution is increased by adding 2 oz. of NaCl, or 12-14 oz. of NaCl to each gallon. Pocket-handkerchiefs must be avoided, linen rags being employed instead, and placed at once in one of the above solutions or burnt.

The =skin= may scatter infection, especially in small-pox and scarlet fever. Frequent baths and inunction with vaseline or oil are useful.

The =disinfection of hands= is most important for all attendants on the infectious sick. A solution of corrosive sublimate 1-1000, or one of the above solutions may be used for this purpose; but this is to be supplemented by the free use of the nail-brush and soap and water. The treatment of =linen= has been described (page 329).

=Woollen articles= of underclothing, and =blankets= can be disinfected by steam, which shrinks them less than boiling water. The ordinary laundry processes appear, however, to suffice to rid them of infection, without boiling.

=Bedding=, curtains, and carpets should be disinfected by steam. Certain precautions are required in removing these to the disinfecting station. Surface disinfection of the room must have been first effected (see below); and the infected bedding should be encased in canvas bags or sheets. When a steam disinfector is inaccessible, the mattress and pillows should be taken to pieces, the covers washed, and their contents disinfected by spraying with formalin solution (1 in 40) or HgCl₂ solution (1 in 1,000), and subsequently exposing to sun and air. For disinfection of suits of clothes, current steam may be improvised as follows:—Over two bricks at the bottom of the kitchen “copper” thin floor-boards are placed, above the level of 2 or 3 inches of water previously placed at the bottom of the copper. The cover of the copper is put on, and by means of a brisk fire steam is kept streaming through the clothes. This is continued for an hour, and the clothes then hung out to dry.

=Furniture=, when wooden, can be washed. If upholstered it can be disinfected by spraying (see p. 333), and then beating and dusting in the open air.

=Furs, Boots, and Shoes= are spoilt by steam. For the first, spraying freely with formalin (1 in 40), or exposure over a formalin lamp (page 326) is recommended. Boots and shoes should be filled and washed with a solution of HgCl₂, chinosol, or formalin.

The =sick-room= can only be efficiently disinfected after the patient has left it. The aim is _surface disinfection_. Aerial disinfection is sufficiently effected by open windows. Four chief methods of surface disinfection are practised. (_a_) _Fumigation_ by SO₂, formalin, cresol, or other vapours (see page 326). (_b_) _Spraying_ the ceiling, walls, floor, and furniture with a disinfectant solution is probably the most convenient method of disinfection. It is more effectual than fumigation, less laborious than rubbing down walls, etc., by bread or wet cloth, and less likely to damage wall-papers than brushing a disinfectant solution on them. Solutions of HgCl₂ 1 in 1,000, or chinosol 1 in 1,200, or formalin 1 in 40 are efficient. A special spray apparatus (Fig. 58) is usually employed. A practical point is to spray the wall from below upwards, to prevent the solution running down the wall and producing streaks of discolouration. (_c_) _Washing_ ceiling and walls with the disinfectant solution may be substituted. A one per cent. solution of hypochlorite of lime is largely used for this purpose, applied by a long-handled whitewash brush. (_d_) _Attrition_ of walls, etc., by means of bread or dough sterilises them by mechanically removing microbes. The bread is cut into pieces suitable for grasping in the hand, the cut surface being applied to the wall. The crumbs must afterwards be burnt in the room. This is the official method in Germany.

=Floors= may be treated like walls and ceiling after the patient has left the room. During his occupancy of the room, tea-leaves or sawdust thoroughly impregnated with lysol or cresol should be sprinkled on the floor before it is swept, or washing substituted for sweeping. Scrubbing with soap and water constitutes the best disinfectant for floors and all other washable surfaces.

=Books= are difficult of disinfection. Steam damages leather. The penetrating power of dry heat is doubtful. Cheap books should be burnt. Abel discovered virulent diphtheria bacilli on toys six months after the patient, to whom they belonged, had diphtheria. Formalin and phenol vapours have been used to disinfect books in closed chambers, the books being stood on end. Letters can be rendered safe by steam disinfection.

=Corpses= of infectious patients should be placed in the coffin and buried as early as possible. A thick layer of sawdust saturated with lysol or cresol should be placed at the bottom of the coffin, and the corpse enveloped in cotton wool. Cremation is better than burial.