CHAPTER IX

_DISINFECTION_

The object of modern bacteriology is not merely to accumulate tested

facts of knowledge, nor only to learn the truth respecting the biology

and life-history of bacteria. These are most important things from a

scientific point of view. But they are also a means to an end; that

end is the prevention of preventable diseases and the treatment of any

departure from health. In a science not a quarter of a century old much

has already been accomplished in this direction. The knowledge acquired

of, and the secrets learned from, these tiny vegetable cells which have

such potentiality for good or evil have been, in some degree, turned

against them. When we know what favours their growth and vitality and

virulence, we know something of the physical conditions which are

inimical to their life; when we know how to grow them, we also know how

to kill them.

We have previously made a cursory examination of the methods which are

adopted for opposing bacteria and their products in the tissues and

body fluids. We must now turn to consider shortly the modes which may

be adopted in preventive medicine for opposing bacteria outside the

body.

It will be clear at once that we may have varying degrees of

opposition to bacteria. Some substances kill bacteria, and they are

known as _germicides_; other substances prevent their development and

resulting septic action, and these are termed _antiseptics_. The

word _disinfectant_ is used more or less indiscriminately to cover

both these terms. A _deodorant_ is, of course, a substance removing

the odour of evil-smelling putrefactive processes. Here, then, we

have the common designations of substances able to act injuriously on

bacteria and their products outside, or upon the surface of, the body.

But a moment's reflection will bring to our minds two facts not to be

forgotten. In the first place, an antiseptic applied in very strong

dose, or for an extended period, may act as a germicide; and, _vice

versâ_, a germicide in too weak solution to act as such may perform

only the function of an antiseptic. Moreover, the action of these

disinfecting substances not only varies according to their own strength

and mode of application, but it varies also according to the specific

resistance of the protoplasm of the bacteria in question. Examples

of the latter are abundant, and readers who have only assimilated

the simple facts set forth in these pages are aware that between the

bacillus of diphtheria and the spores of anthrax there is an enormous

difference in power of resistance. In the second place, reflection

will enable us to recall what has already been said, when discussing

the requirements necessary for bacterial growth, respecting the

physical conditions injurious to development. In a _cold temperature_,

as a general rule, bacteria do not multiply with the same rapidity

as at blood-heat. Within the limits of a _moist perimeter_ the air

is, to all intents and purposes, germ-free. Direct _sunlight_ has a

definitely germicidal effect in the course of time upon some of the

most virulent bacteria we know. Here, then, are three examples of

physical agents--low temperature, moist perimeter, sunlight--which, if

strong enough in degree, or acting for a long enough period of time,

become first antiseptics and then germicides. Yet for a limited period

they have no injurious effect upon bacteria. These are simple points,

and call for little comment, yet the pages of medical and sanitary

journals reveal not a few keen controversies upon the injurious action

of certain substances upon certain bacteria owing to the discrepancies,

of necessity arising, between results of different skilled observers

who have been carrying out different experiments with different

solutions of the same substance upon different protoplasms of the

same species of bacteria. We feel no doubt that in these pioneering

researches much labour has been to some extent misspent, owing to the

neglect of a common denominator. Only a more accurate knowledge of

bacteria or a recognised standard for disinfecting experiments can ever

supply such common denominator.

Species of bacteria for comparative observation-experiments upon

the action of chemical or physical agents must be not only the same

species, but cultured under the same conditions, and treated by the

agent in the same manner, otherwise the results cannot be compared upon

a common platform, or with any hope of arriving at exactly the same

conclusions.

Sir George Buchanan laid down, in 1884, a very simple and suitable

standard of what true disinfection meant, viz., the _destruction of the

most stable known infective matter_. Such a test is high and difficult

to attain unto; nevertheless, it is the only satisfactory one.

Obviously many substances which are useful antiseptics in practical

life would fall far short of such a standard, yet for true and complete

disinfection such an ideal is the only adequate one.

Quite recently three or four workers at Leipzig[101] have drawn up

simple directions, the adoption of which would considerably assist

in securing a common standard for disinfectant research. They are as

follows:

1. In all comparative observations it is imperative that _molecularly

equivalent_ quantities of the reagents should be employed.

2. The bacteria serving as test objects should have equal power of

resistance.

3. The numbers of bacteria used in comparative observation should be

approximately equal.

4. The disinfecting solution must be always used at the same

temperature in comparative experiments.

5. The bacteria must be brought into contact with the disinfectant with

as little as possible of the nutrient material carried over. (This

obviously will depend upon the object of the research.)

6. After having been exposed to the disinfectant for a fixed time, they

should be freed from it as far as possible.

7. They should then be returned in equal numbers to the respective

culture medium most favourable to the development of each, and kept at

the same, preferably the optimum, temperature for their growth.

8. The number of surviving bacteria capable of giving rise to colonies

in solid media must be estimated after the lapse of equal periods of

time.

We may now turn from general principles to mention shortly some of

the commoner methods and substances adopted to secure efficient

disinfection. They are all divisible, according to Sir George

Buchanan's standard, into two groups:

1. Heat in various forms;

2. Chemical bodies in various forms.

It should at the outset be understood that we desire in practical

disinfection to inhibit or kill micro-organisms without injury to, or

destruction of, the substance harbouring the germs for the time being.

If this latter is of no moment, as in rags or carcasses, burning is the

simplest and most thorough treatment. But with mattresses and beddings,

bedclothes and garments, as well as with the human body, it is obvious

that something short of burning is required.

1. From the earliest days of bacteriology heat has held a prominent

place as a disinfector. But it is only in comparatively recent times

that it has been fully established that _moist heat_ is the only really

efficient form of heat disinfection. Boiling at atmospheric pressure

(100° C.) is the oldest form of moist heat disinfection, and because

of the simplicity of its application it has gained a large degree of

popularity. But it must not be forgotten that mere boiling (100° C.)

may not effectually remove the spores of all bacilli. Besides, boiling

is not applicable to furniture, mattresses, and such-like frequently

infected objects. For many of these _hot-air ovens_ were used in the

early days. But it was found that such disinfection was no disinfection

at all, for not only did it leave many organisms and spores untouched,

but the degree of temperature was rarely, if ever, uniform throughout

the substance being treated.

The failures following in the track of these methods were an indication

of the need of some form of moist heat, viz., steam.

Here it will be necessary to digress for a moment into some of the

characters of steam. When water is heated certain molecular changes

take place, and at a certain temperature (100° C., 212° F.) the water

becomes steam, or _vapour_, and on very little cooling will condense.

But if the vapour is heated, it will become practically a gas, and

will not condense until it has lost the whole of the heat, _i. e._,

the heat of making water into vapour plus the heat of making vapour

into gas. A gas proper is, then, the vapour of a liquid of which the

boiling-point is substantially below its actual temperature. But we

know that the temperature at which it boils depends upon the pressure

to which it is subjected (Regnault's law). Hence in reality "steam at

any temperature whatever may be a vapour proper, provided the pressure

is such as prevents the liquid from boiling below that temperature."

In such a condition of vapour it is termed _saturated steam_. But if

it is at that same pressure further heated, it becomes practically a

gas, and is called _superheated steam_. The former can condense without

cooling; the latter cannot so condense at the same pressure. Saturated

steam condenses immediately it meets the object to be disinfected,

and gives out its latent heat; superheated steam acts by conduction,

and not uniformly throughout the object. Its advantage is that it

dries moistened objects. As a disinfecting power, superheated steam

is much less than saturated steam. There is one further term which

must be defined, namely, _current steam_. This is steam escaping from

a disinfector as fast as it is admitted, and may be at atmospheric or

higher temperatures. The disinfecting temperature which is now used as

a standard is _an exposure to saturated steam of 115° C. for fifteen

minutes_.

A number of different kinds of apparatus have been invented to

facilitate disinfection to this standard on a large scale. Most

sanitary authorities of importance are now supplied with some form

of steam disinfector, though many are unable to go to the expense of

high-pressure disinfectors. Professor Delépine has pointed out[102]

that a current of steam at low pressure may completely disinfect.

Whilst such simple current-steam machines have thus been demonstrated

as efficient bactericides, for all practical purposes it is important

to have disinfectors capable of giving temperatures considerably

above 100° C., of simple construction, having steam power of uniform

temperature and rapid penetration, and containing, when in action, a

minimum of superheated steam. In addition to these characters of a

first-rate steam disinfector, two other important points should be

borne in mind, namely, the air must be completely ejected from the

disinfection chamber before the results due to steam are obtained, and

some sort of automatic index giving a record of each disinfection is

indispensable.

We may turn from these general principles to mention shortly some of

the types of steam disinfectors most commonly in use. They are four,

namely, the Washington Lyon, the Equifex (Defries), the Thresh, and the

Reck.

_Washington Lyon's_ apparatus consists of an elongated boiler having

double walls, with a door at each end. The body of the apparatus is

jacketed. The whole is large enough to admit of bedding and mattresses,

and generally is so arranged that one end opens into one room, and

the other end opens into another room. This convenient position

admits of inserting infected articles from one room and receiving

them disinfected into the other room. Possible reinfection is thereby

prevented. Steam is admitted into the jacket at a pressure of between

twenty and twenty-five pounds, and is generally twenty pounds in the

interior of the cylinder. At the end of the operation a partial vacuum

is created, by which means much of the moisture on the articles may

be removed. In some cases a current of warm air is admitted before

disinfection in order to diminish the extent of condensation.

The _Equifex_ (Defries) contains no steam jacket, but coils of pipes

are placed at the top and bottom of the apparatus, with the object

of imparting to the steam as much heat as is lost by radiation

through the walls of the disinfecting chamber, and at the same time

of preventing undue condensation. The air is first removed by a

preliminary current of steam, after which steam at a pressure of ten

pounds is intermittently introduced and allowed to escape. The object

of this proceeding is to remove air from the pores of the articles to

be disinfected by the sudden expansion of the film of water previously

condensed on their surface. The apparatus introduced by _Dr. Thresh_

was constructed with a view of overcoming the objection to some of

the other machines that bulky articles retained a large percentage

of moisture, thus necessitating the use of some additional drying

apparatus. A central chamber receives the articles to be disinfected,

and is surrounded by a boiler containing a solution of calcium chloride

at a temperature of 225° F. This is heated by a small furnace, and

the steam given off (218-300° F.) is conducted into the central

chamber. The steam is not confined under any pressure except that of

the atmosphere. When the steam has passed for a sufficient length

of time, it is readily diverted into the open air. Hot air is now

introduced, and at the expiration of an hour the articles may be taken

out disinfected and as dry as they were when inserted. The apparatus

is comparatively inexpensive, and not of a complicated nature. The

current steam is saturated, and at a temperature a few degrees above

the boiling-point. Many experiments have been performed with this

apparatus, and there is now a large amount of evidence in favour of it

and current steam disinfection.

_Reck's_ apparatus is another kind of saturated steam disinfector,

which resembles the Equifex, but differs from it in employing steam as

a current.

It is probable that many other forms of steam disinfector will be

invented, and each will have its enthusiastic supporters. Even at the

time of writing some excellent results are announced from America.

2. The effects of _chemical substances_ as solutions, or in spray

form, upon bacteria have been observed from the earliest days of

bacteriology. To some decomposing matter or solution a disinfectant

was added and sub-cultures made. If bacteria continued to develop,

the disinfection had not been efficient; if, on the other hand, the

sub-culture remained sterile, disinfection had been complete. From such

rough-and-ready methods large deductions were drawn, and it is hardly

too much to say that no branch of bacteriology contains such a vast

mass of unassimilated and unassimilable statements as that relating to

research into disinfectants. Most of the tabulated and recorded results

are conspicuous in having no standard as regards bacterial growth. Yet

without such a standard results are not comparable.

Silk threads, impregnated with anthrax spores, were placed in bottles

containing carbolic acid of various strengths, and at stated periods

threads were removed and placed in nutrient media, and development or

otherwise observed. But, as Professor Crookshank[103] has pointed out,

this method is fallacious, the thread being still wet with the solution

when transferred to the medium, and thus modified in culture, possibly

even inhibited altogether. It is unnecessary for us here to discuss

every mode adopted by investigators in similar researches. We may just

mention that the most approved methods at the present time are based

upon two simple plans of exposure. In one we use a known volume of

recent broth culture of an organism grown under specified conditions.

To this is added a measured quantity of the antiseptic. At stated

periods loopfuls of the broth and antiseptic mixture are sub-cultured

in fresh-sterilised broth, and resulting development or otherwise

closely observed. The other method is practicable when we are dealing

with volatile bodies. In such cases a standard culture is made of the

organism in broth at a standard temperature. Into this are dipped

small strips of sterilised linen. When thoroughly impregnated these

are removed from the broth and subsequently dried over sulphuric acid

in a vacuum at 38° C. These may now be exposed for a longer or shorter

period to the fumes of the antiseptic in question, and broth cultures

made at the end of the exposure. It is obvious that a very large number

of modifications are possible of these two simple devices for testing

the bactericidal power of chemical substances. It should be remembered

that here, perhaps, more than anywhere else in bacteriological

research, careful control experiments are absolutely necessary.

_Mineral acids_ (nitric, hydrochloric, sulphuric), especially

concentrated, are all germicides.

The _halogens_--chlorine, bromine, iodine, and fluorine--are, all four,

disinfectants, but not used in practice. They are named in their order

of power as such.

A number of separate bodies, such as _chloroform_ and _iodoform_, have

been much advocated as antiseptics. The cost of the former and odour

of the latter have, however, greatly militated against their general

adoption.

_Chloride of lime_ is a powerful disinfectant. Professor Sheridan

Delépine and Dr. Arthur Ransome have demonstrated its germicidal

effect as a solution applied directly to the walls of rooms inhabited

by tuberculous patients.[104] It may also be used in solid form for

dusting decomposing matter.

_Mercuric chloride_ (corrosive sublimate) has been an accepted

germicide for some time. But the experiments of Behring, Crookshank,

and others have proved that the weaker solutions cannot be relied

upon. This is, in part, due to the fact that it forms in albuminous

liquids an albuminate of mercury which is inactive. Dilute solutions

have the further disadvantage of being unstable. Various authorities

recommend a solution of 1-500 as a germicide, and much weaker solutions

are, of course, antiseptic. An ounce each of corrosive sublimate

and hydrochloric acid in three gallons of water makes an efficient

disinfectant.

_Potassium permanganate_ is, of course, the chief substance in Condy's

fluid, as _zinc chloride_ is in Burnett's disinfecting fluid. A 5 per

cent. of the former and a 2-1/2 per cent. of the latter are germicidal.

_Boracic acid_ is one of the most useful antiseptics with which to

wash sore eyes, or preserve tinned foods or milk. It is not a strong

germicide, but an unirritating and effective wash. Many cases of its

addition to milk have found their way into the law courts, owing to

cumulative poisoning, and it should only be used with the very greatest

care as a food preservative.

_Carbolic acid_ has come into prominence as an antiseptic since its

adoption by Lister in antiseptic surgery. It is cheap, volatile, and

effective. One part in 400 is antiseptic, and 1 in 20 germicidal. As

a wash for the hands the former is used, and a weaker solution for

the body generally. Carbolic soap and similar toilet combinations are

now very common. At one time it appeared as if corrosive sublimate

would oust carbolic from the first place as an antiseptic solution,

but a large number of experiments have confirmed opinion in favour

of carbolic. Professor Crookshank found that carbolic acid, 1 in 40,

acting for only one minute is sufficient to destroy _Streptococcus

pyogenes_, _S. erysipelatis_, and _Staphylococcus pyogenes aureus_,

and in the strength of 1 in 20 carbolic acid completely sterilised

tubercular sputum when shaken up with it for one minute.

_Creosol_, a member of the phenol series, is a good disinfectant, and

the active element in lysol, Jeye's fluid, creoline, izal, and creosote.

_Sulphurous acid_ is one of the commonest disinfectants employed for

fumigation--the old orthodox method of disinfecting a room in which a

case of infective disease has been nursed. It is evolved, of course, by

burning sulphur. For each thousand cubic feet from one to five pounds

of sulphur is used, and the walls may be washed with carbolic acid.

Dr. Kenwood carried out some experiments in 1896[105] which appear to

support the disinfecting power of sulphur fumes. He found that the

_Bacillus diphtheriæ_ was not killed, though markedly inhibited, when

the sulphurous gas (SO_{2}) did not much exceed .25 per cent. But the

bacillus was killed where the sulphur fumes exceeded .5 per cent. Both

these results had reference to the SO_{2} in the air in the centre of

the room at a height of four feet, and after the lapse of four hours.

There can be little doubt that fuming a sealed-up room with sulphur

fumes in a moist atmosphere, and leaving it thus for twenty-four hours,

is generally, if not always, efficient disinfection. It will kill

the bacillus of diphtheria, though not always more resistant germs.

Moreover, its simplicity of adoption is greatly in its favour. Anyone

can readily apply it by purchasing a few pounds weight of ordinary roll

sulphur and burning this in a saucer in the middle of a room which has

had all its crevices and cracks in windows and walls blocked up with

pasted paper. _Nitrous fumes_ may also be used in this way.

Recently _formalin_ has come much in favour as a room disinfectant.

Formalin is a 40 per cent. solution of formaldehyde in water, a gas

discovered by Hofmann in 1869. This gas is a product of imperfect

oxidation of methyl alcohol, and may be obtained by passing vapour

of methyl alcohol, mixed with air, over a glowing platinum wire or

other heated metals, such as copper and silver. It is the simplest

of a series of aldehydes, the highest of which is palmitic aldehyde.

Its formula is CH_{2}O, and it is a colourless gas with a pungent

odour, and having penetrating and irritating properties, particularly

affecting the nasal mucous membrane and the eyes of those working with

it. It is readily soluble in water, and in the air oxidises into formic

acid (CH_{2}O_{2}). This latter substance occurs in the stings of bees,

wasps, nettles, and various poisonous animal secretions. Formalin

is a strong bactericide even in dilute solutions, and, of course,

volatile. A solution of 1 to 10,000 is said to be able to destroy

the bacilli of typhoid, cholera, and anthrax. A teaspoonful to ten

gallons of milk is said to retard souring. When formalin is evaporated

down, a white residue is left known as paraform. In lozenge form this

latter body is used by combustion of methylated spirit to produce the

gas. Hence we have three common forms of the same thing--_formalin_,

_formic aldehyde_, _paraform_--each of which yields _formic acid_, and

thus disinfects. The vapour cannot in practice be generated from the

formalin as readily as from the paraform.

By a variety of ingenious arrangements formic aldehyde has been tested

by a large number of observers during the last two or three years. We

may refer to three modes of application. 1. _The sprayer_ (Equifex

apparatus) produces a mixture of air and solution for spraying walls,

ceilings, floors, and sometimes garments. 2. _The autoclave_ (Trillat's

apparatus). In this a mixture of a 30-40 per cent. watery solution

of formaldehyde and calcium chloride (4-5 per cent.) is heated under

a pressure of three or four atmospheres, and the almost pure, dry

gas is conducted through a tube passing through the keyhole of the

door into the sealed-up room. 3. _The paraform lamp_ (the Alformant).

The principle of this lamp is that the hot, moist products from

the combustion of methylated spirit act upon the paraform tablets,

converting them into gas. Most of the conclusions derived from

experiments with these three different forms of apparatus are the same.

It is agreed that the gas is harmless to colours and metal and polished

wood. The vapour acts best in a warm atmosphere. As for its action on

bacteria, it compares favourably with any other disinfectant. In 1 per

cent. solution formalin destroys non-spore-bearing bacteria in thirty

to sixty minutes.

Many observers have decried formaldehyde on account of its professed

lack of penetrating power. Professor Delépine, however, states[106]

that it possesses "penetration powers probably greater than those

of most other active gaseous disinfectants. _Bacillus coli_, _B.

tuberculosis_, _B. pyocyaneus_, and _Staph. pyogenes aureus_ were

killed in dry or moist state, even when protected by three layers of

filter paper." In Professor Delépine's opinion, the vapours of

phenol, izal, dry chlorine, and sulphurous acid have, under the same

conditions, given inferior results.

We may now shortly summarise the foregoing facts respecting antiseptics

and disinfection in the simplest terms possible to afford facility to

the uninitiated in practical application:

_To disinfect a room_, seal up cracks and crevices, and burn at least

one pound of roll sulphur for every 1,000 cubic feet of space.[107]

Many authorities recommend four or five pounds of sulphur to the same

space. Let the room remain sealed up for twenty-four hours.

_To disinfect walls_, wash with chloride of lime solution (1-100) or

carbolic acid (1-40). This latter solution may be used to wipe down

furniture. Either or both may be used _after_ sulphur fuming. Formic

aldehyde may also be used by lamp or autoclave.

_To disinfect bedding_, _etc._, the steam sterilisation secured in

a Thresh, Equifex, or Lyon apparatus is the best. Rags and infected

clothing, unless valuable, should be burnt.

_To disinfect garments and wearing apparel_, they should be washed in a

disinfectant solution, or fumed with formic aldehyde.

_To disinfect excreta or putrefying solutions_, enough disinfectant

should be added to produce _in the solution or matter being

disinfected_ the percentage of disinfectant necessary to act as such.

Adding a small quantity of antiseptic to a large volume of fluid or

solid is as useless as pouring a small quantity of antiseptic down a

sewer with the idea that such treatment will disinfect the sewage. The

mixture of the disinfectant with the matter to be disinfected must

contain the standard percentage for disinfection. Chloride of lime is a

common substance for use in this way. Potassium permanganate (1-100)

and carbolic (1-100), and many manufactured bodies containing them, are

also widely used. Drs. Hill and Abram recommend[108] that the excreta

and disinfectant be thoroughly mixed and stand for at least half an

hour. For various reasons they particularly advise _chinosol_ as the

most convenient disinfectant for this specific purpose.

_Antiseptics for wounds._ Carbolic acid (1-40) or corrosive sublimate

(1-1,000) are commonly used in surgical practice. Boracic acid is one

of the most unirritating antiseptics which are known. It may be used in

saturated watery solution (1-30) or dusted on copiously as fine powder.

It is especially applicable in open wounds, and as an eye-wash.

_To disinfect hands and arms._ Operating surgeons are those to whom it

is a most urgent necessity to cleanse hands and arms antiseptically.

Carbolic acid (1-20, or 1-40) is used for this purpose.

It is hardly necessary to add that in a case of infectious disease

occurring in a household many of these modes of application, perhaps

all of them, must be adopted. Formalin is probably the best gaseous

disinfectant which we have, but its use does not, and should not,

preclude the simultaneous adoption of other methods.

APPENDIX

It is proposed to add one or two notes on certain technical points in

bacteriological work, with a view to assisting those medical men not

able to obtain the advantages of a well-equipped laboratory, and yet

desirous of occasionally attempting some practical bacteriology.

1. _General Examination._ All fluids may be examined for bacteria in

two chief ways:

(_a_) A small quantity may be placed on a cover-glass or slide, dried

over a lamp or bunsen flame, and stained with aniline dyes for a few

minutes. It is then ready for microscopic examination. It is obvious

that the result will generally be a _mixture_ of bacteria, for which

differentiating stains may be used (Gram, Ziehl-Neelsen, etc.).

(_b_) A minute drop of the suspected fluid may be added to various

fluid media (broth, liquefied gelatine, etc.) and then plated out

upon small sterilised sheets of glass. In the course of two or three

days the contained bacteria will reveal themselves in characteristic

colonies, which may be examined, and if possible sub-cultured, and

carefully studied.

_Double-Staining Methods._ These are various, and are used when it is

desired to stain the bacteria themselves one colour, and the matrix or

ground substance in which they are situated another colour. Three of

the commoner methods are those of Ehrlich, Neelsen, and Gram. They are

as follows:

_Ehrlich's Method._ "Five parts of aniline oil are shaken up with

100 parts distilled water, and the emulsion filtered through

moistened filter paper. A saturated alcoholic solution of fuchsine,

methyl-violet, or gentian-violet is added to the filtrate in a

watch-glass, drop by drop, until precipitation commences. Cover-glass

preparations are floated in this mixture for fifteen to thirty minutes,

then washed for a few seconds in dilute nitric acid (one part nitric

acid to two of water), and then rinsed in distilled water. The stain is

removed from everything except the bacilli; but the ground substance

can be after-stained brown if the bacilli are violet, or blue if

they have been stained red" (Crookshank, _Bacteriology and Infective

Diseases_, p. 89).

_Gram's Method._ The primary stain in this method is a solution of

aniline gentian-violet (saturated alcoholic solution of gentian-violet

30 cc., aniline water 100 cc.), which stains both ground substance and

bacteria in purple. The preparation is next immersed in the following

solution for half a minute or a little more:

Iodine 1 part

Potassium iodide 2 parts

Distilled water 300 parts

In this short space of time the iodine solution acts as a mordant of

the purple colour in the bacteria, but not in the ground substance.

Hence, if the preparation be now (when it has assumed a _brown_

colour) washed in alcohol (methylated spirit), the ground substance

slowly loses its colour and becomes clear. But the bacteria retain

their colour, and thus stand out in a well-defined manner. Cover-glass

preparations decolourise more quickly than sections of hardened tissue,

and they should only be left in the methylated spirit until no more

colour comes away. The preparation may now be washed in water, dried,

and mounted for microscopic examination, or it may be double-stained,

that is, immersed in some contrast colour which will lightly stain the

ground substance. Eosin or Bismarck brown are commonly used for this

purpose. The former is applied for a minute or two, the latter for

five minutes, after which the specimen is passed through methylated

spirit (and preferably xylol also) and mounted. The result is that the

bacteria appear in a dark purple colour on a background of faint pink

or brown. Carbol-thionine blue, picro-carmine, and other stains are

occasionally used in place of the aniline gentian-violet, and there

are other slight modifications of the method.

_Ziehl-Neelsen Method._ Here the primary stain is a solution of

carbol-fuchsin:

Fuchsin 1 part

Absolute alcohol 10 parts

5 per cent. aqueous solution of carbolic acid 100 parts

It is best to heat the dye in a sand-bath, in order to distribute the

heat evenly. The various stages in the staining process are as follows:

(_a_) The cover-glass with the dried film upon it is immersed in the

hot stain for one to three minutes. (_b_) Remove the cover-glass from

the carbol-fuchsin, and place it in a capsule containing a 25 per cent.

solution of sulphuric acid to decolourise it. Here its redness is

changed into a slate-grey colour. (_c_) Wash in water, and alternately

in the acid and water, until it is of a faint pink colour. (_d_) Now

place the cover-glass for a minute or two in a saturated aqueous

solution of methylene-blue, which will counter-stain the decolourised

ground substance blue. (_e_) Wash in water. (_f_) Dehydrate by rinsing

in methylated spirit, dry, and mount. A pure culture of bacteria will

not necessarily require the counter-stain (methylene-blue). Sections

of tissue may require twenty to thirty minutes in the primary stain

(carbol-fuchsin). This stain is used for tubercle and leprosy. With

a little practice the staining of the bacillus of tubercle when

present in pus or sputum becomes a very simple and accurate method of

diagnosis. A small particle of sputum or pus is placed between two

clean cover-glasses and thus pressed between the thumb and finger into

a thin film. This is readily dried and stained as above, the bacillus

of tubercle appearing as a delicately-beaded red rod with a background

of blue.

_Bacteriological Diagnosis._ The following points must be ascertained

in order to identify any particular micro-organism:

(1) Its morphology, bacillus, coccus, spirillum, etc.; the presence or

absence of involution forms.

(2) Motility by the unstained cover-glass preparation ("hanging drop");

note presence of flagella.

(3) Presence of spores, their appearance and position.

(4) Whether or not the organism stains with Gram's method.

(5) The character of the growth upon various media (gelatine, agar,

milk, potato, broth); the presence or absence of liquefaction in the

gelatine culture; its power of producing acid, gas, or indol.

(6) Whether it is aërobic or anaërobic.

(7) Its colour in cultivation.

(8) If it is a disease-producing organism under examination, its

effect upon the animal tissues and the course of the disease should be

observed.

There are other points of importance, but the above are essential to a

right conclusion.

_Diagnosis in Special Diseases:_

(1) _Diphtheria._ This disease may be bacteriologically diagnosed with

a minimum of apparatus and equipment. By means of a swab a rubbing

from a suspected throat is readily obtained. This may be examined by

the microscope, or sub-cultured on favourable medium. Blood serum is

perhaps the best, but, as Hewlett remarks, "If no serum tubes can be

had, an egg may be used. It is boiled hard, the shell chipped away from

one end with a knife sterilised by heating, and the inoculation made

on the exposed white surface; the egg is then placed, inoculated end

down, in a wine-glass of such a size that it rests on the rim and does

not touch the bottom. A few drops of water may with advantage be put at

the bottom of the glass to keep the egg-white moist. The preparation

is kept in a warm place for twenty-four to forty-eight hours and

then examined." The examination, of course, consists in staining and

preparing for the microscope and observing the form, arrangement, and

characters of the organism or organisms present. A small piece of the

membrane may be detached, washed in water, and stained for the bacilli.

(2) _Tubercle_ (Ziehl-Neelsen's stain, _vide supra_).

(3) _Typhoid_ (_Enteric Fever_).

_Widal's Reaction._ This diagnostic test depends upon the effect

which the blood of a person suffering from typhoid fever has upon the

_Bacillus typhosus_. The effect is twofold. In the first place, the

actively motile _B. typhosus_ becomes immotile; and secondly, there

is an agglutination, or grouping together in colonies, of the _B.

typhosus_. Neither of these features occurs if healthy human blood is

brought into contact with a culture of the typhoid bacillus. There

are various ways in which this "serum diagnosis" can be carried out.

The simplest and quickest method is as follows: To ten drops of a

twenty-four or forty-eight-hours-old neutral broth culture of the

typhoid bacillus one drop of the blood serum to be tested is added.

The serum and culture are rapidly mixed in the trough of a hollow

ground slide (such as is used for the "hanging drop"), and a single

drop is taken, placed upon an ordinary clean slide, and a cover-glass

superimposed. The positive reaction of agglutination and immotility,

if the blood comes from a case of typhoid fever, will probably appear

within fifteen or twenty minutes. The fluid culture of typhoid may be

taken from an agar culture as well as from broth. In both cases it may

be desirable to filter through ordinary filter paper to remove any

normally agglutinated masses of bacilli before commencing the test.

In his first experiments Widal used a test-tube in the following

manner: The blood to be tested is diluted by one part of it being added

to fifteen parts of broth in a test-tube. The mixture is inoculated

with a drop of a typical _Bacillus typhosus_ culture. The tube is then

incubated at 37° C. for twenty-four hours, after which it is examined.

If the reaction be positive, the broth appears comparatively clear, but

at the bottom of the test-tube a more or less abundant sediment will

be found. This is due to the clumps of bacilli having fallen owing to

gravity. If, on the other hand, the reaction is negative, the broth

will appear more or less uniformly turbid.

For the _apparatus_ required to carry out the simpler methods of

bacteriological work reference should be made to the standard

laboratory text-books, which furnish all necessary details. A good

microscope, with a 1/12 oil immersion lens, is, of course, essential.

This can now be obtained for about £16 (Beck, Swift, Baker, Watson,

etc.), and the other necessary apparatus is readily obtainable of Baird

and Tatlock, Hatton Garden, E. C., and other makers.

FOOTNOTES:

[1] _The Contemporary Review_, November, 1897, p. 719.

[2] Some notable exceptions are found in the work of the Bath

and West of England Society, Lord Vernon's model dairy, and

the Essex County Council Bacteriological Teaching Laboratory.

[3] We propose throughout to use the term _bacterium_ (pl.

_bacteria_) in its generic meaning, unless especially stated

to the contrary. It will also be synonymous with the terms

_microbe_, _germ_, and _micro-organism_. The term _bacillus_

will, of course, be restricted to a rod-shaped bacterium.

[4] Migula has recently (1896) suggested that the

Schizomycetes should be subdivided into _Coccaceæ_,

_Bacteriaceæ_, _Spirillaceæ_ (spirilla, spirochæta),

_Chlamydobacteriaceæ_ (Streptothrix, Crenothrix, Cladothrix),

and _Beggiatoa_.

[5] A one-twelfth oil immersion lens is requisite for the

study of the lower bacteria.

[6] A _flagellum_ is a hair-like process arising from the

poles or sides of the bacillus. It must not be confused with

a _filament_, which is a thread-like growth of the bacillus

itself.

[7] A "pure culture" is a growth in an artificial medium

outside the body of one species of micro-organism only.

[8] Some pathogenic germs (suppuration and typhoid) can

withstand freezing for weeks.

[9] G. J. Romanes, _Darwin and After Darwin_, vol. ii., 231.

[10] It will be observed that there is a marked difference

between the effects of dry heat and moist heat. Moist heat is

able to kill organisms much more readily than dry, owing to

its penetrating effect on the capsule of the bacillus. Dry

heat at 140° C. (284° F.), maintained for three hours, is

necessary to kill the resistant spores of _Bacillus anthracis_

and _B. subtilis_, but moist heat at fifty degrees less will

have the same effect. It is from data such as these that in

laboratories and in disinfecting apparatus moist heat is

invariably preferred to dry heat. For with the latter such

high temperatures would be required that they would damage the

articles being disinfected. Koch states the following figures

for general guidance: Dry heat at a temperature of 120° C.

(248° F.) will destroy spores of mould fungi, micrococci,

and bacilli in the absence of their spores; for the spores

of bacilli 140° C. (284° F.), maintained for three hours, is

necessary; moist heat at 100° C. (212° F.) for fifteen minutes

will kill bacilli and their spores.

[11] Water from a house cistern is rarely a fair sample. It

should be taken from the main. If taken from a stream or still

water, the collecting bottle should be held about a foot below

the surface before the stopper is removed.

[12] The _cubic centimetre_ (cc.) is a convenient standard of

fluid measurement constantly recurring in bacteriology. It is

equal to 16-20 drops, and 28 cc. equal one fluid ounce.

[13] The gelatine is reduced to liquid form by heating in

a water-bath. Before inserting the suspected water it is

essential that the gelatine be under 40° C, or thereabouts, in

order not to approach the thermal death-point of any bacteria.

[14] _Micro-organisms in Water_ (1894).

[15] Report on the Micro-organisms of Sewage, Reports to L. C.

C., 1894, No. 216.

[16] Harben Lectures, 1896.

[17] Report on the Metropolitan Water Supply.

[18] The methods adopted for making a quantitative and

qualitative examination of sewage are precisely analogous

to those used in milk research. Dilution with sterilised

water previous to plating out on gelatine in Petri dishes

is essential (1 cc. to 10,000 cc. of sterile water, or some

equally considerable dilution), otherwise the large numbers

of germs would rapidly liquefy and destroy the film. Special

methods must be used for the isolation of special organisms;

phenol-gelatine, Elsner medium, indol reaction, "shake"

cultures, Parietti broth, etc., must often be resorted to for

special bacteria. Spores of bacteria may always be numerically

estimated by adding the suspected water or sewage to gelatine,

and then heating to 80° C. for ten minutes before plating out.

This temperature removes the bacilli, but leaves the spores

untouched.

[19] The bacilli of typhoid can live in crude sewage (Klein),

but only for a very short period. When sewage is diluted

with large quantities of water the case is very different.

_Bacillus coli_ flourishes in sewage.

[20] Annual Report of the Medical Officer of the Local

Government Board, 1897-98, p. 210.

[21] John Tyndall, F.R.S., _Floating Matter of the Air_.

[22] Flügge has lately attempted to demonstrate that an air

current having a velocity of four metres per second can remove

bacteria from surfaces of liquids by detaching drops of the

liquid itself.

[23] Hewlett and Thomson graphically demonstrated the

bactericidal power of the nasal mucous membrane by noting

the early removal of _Bacillus prodigiosus_, which had been

purposely placed on the healthy Schneiderian membrane of the

nose.

[24] _Pathological Society of London, Transactions_, 1897.

[25] _Annali d'Igiene Sperimentale_, vol. v. (1895), fasc. 4.

[26] _Public Health_, vol. x., No. 4, p. 130 (1898).

[27] Flügge, _Grundriss der Hygiene_, 1897.

[28] _Zeitschrift für Hygiene_, vols. xxiv.-xxvi.

[29] _Annales de Micrographie._

[30] E. A. Schäfer, F.R.S., _Text-book on Physiology_, vol.

i., p. 312.

[31] The unorganised ferments are frequently otherwise

classified than as above, not according to the locality, but

according to the function. The chief are these:--_amylolytic_,

those which change starch and glycogen (amyloses) into sugars,

_e. g._, ptyalin, diastase, amylopsin; _proteolytic_, those

which change proteids into proteosis and peptones, _e. g._,

trypsin, pepsin; _inversive_, those which change maltose,

sucrose, and lactose into glucose, _e. g._, invertin;

_coagulative_, those which change soluble proteids into

insoluble, _e. g._, rennet; _steatolytic_, those which split

up fats into fatty acids and glycerine, _e. g._, steapsin.

[32] A chemical change obtained by the action of sulphuric or

some other acid, or by the influence of _diastase_.

[33] _Bacteriology and Infective Diseases_, Appendix.

[34] E. C. Hansen, _Studies in Fermentation_ (Copenhagen), p.

98.

[35] _Proc. Royal Soc. of Edin._, xxxvii., pt. iv., p. 759.

[36] E. A. Schäfer, _Text-book of Physiology_, vol. i., p. 25

(W. D. Halliburton).

[37] "Denitrifying" means reducing _nitrates_.

[38] R. Warington, M.A., F.R.S., _Journ. Roy. Agricultural

Soc. Eng._, series iii., vol. viii., pt. iv., pp. 577 _et seq._

[39] The saltpetre beds of Chili and Peru are an excellent

example of the industrial application of these facts. Nitrates

are there produced from the fæcal evacuations of sea-fowl in

such quantities as to form an article of commerce. A like

form of utilisation of the action of these bacteria was once

practiced on the continent of Europe. Economic application is

also seen in the treatment of sewage referred to elsewhere.

[40] The course of nitrification may be followed by means

of chemical tests. 1. The disappearance of ammonia. 2. The

appearance of nitrite. 3. Its disappearance. 4. Appearance of

nitrate.

[41] Professor Warington, in Report IV. (p. 526) of his

admirable series of papers on the subject, draws attention to

Müntz's criticism that the nitrifying organisms only oxidise

from nitrogenous matter to nitrites, and not from nitrites

to nitrates. Müntz held that the conversion of nitrite into

nitrate is brought about by the joint action of carbonic

acid and oxygen. Professor Warington's experiments, however,

clearly illustrate that the production of nitrates from

nitrites in an ammoniacal solution can be determined by the

character of the bacterial culture with which the solution is

seeded, and that in a solution of potassium nitrite conversion

into nitrate can be determined by the introduction of the

nitric organism. Professor Warington still adheres to the

opinion, in favour of which he has produced so much evidence,

that the formation of nitrates in the soil is due to the

nitric organism which soil always contains.

[42] British Association for the Advancement of Science,

Bristol, 1898, Presidential Address.

[43] British Association for the Advancement of Science,

Bristol, 1898, Presidential Address.

[44] Sir John Lawes and Sir Henry Gilbert (_Times_, December

2, 1898), have pointed out that the addition of nitrates only

would be of no permanent use to the wheat crop. They rely upon

thorough tillage and proper rotation of crops as the means of

improving the nitrogen value of the soil.

[45] Geddes, _Nature_, xxv., 1882.

[46] Sir Henry Gilbert, F.R.S., _The Lawes Agricultural Trust

Lectures_, 1893, p. 129.

[47] _Ibid._, p. 140.

[48] This has been denied recently in the official report

by the chemist of the Experimental Farm to the Minister of

Agriculture at Ottawa (_Report_, 1896, p. 200).

[49] It has already been pointed out that the nitrifying

bacteria, though able to live on organic matter, do not

require such either for existence or for the performance of

their function.

[50] Lehmann and Neumann, p. 305.

[51] The conditions requisite for an outbreak of enteric fever

were, according to Pettenkofer, (_a_) a rapid fall (after a

rise) in the ground water, (_b_) pollution of the soil with

animal impurities, (_c_) a certain earth temperature, and

lastly (_d_) a specific micro-organism in the soil. These

four conditions have not, particularly in England, always

been fulfilled preparatory to an epidemic of typhoid. Yet the

observations necessary for these deductions were a definite

step in advance of mere dampness of soil.

[52] _Supplement to the Report of the Medical Officer of the

Local Government Board_, 1887, p. 7.

[53] _Report of Medical Officer to Local Government Board_,

1895-1896, Appendix.

[54] H. L. Russell, _Dairy Bacteriology_, p. 46.

[55] _Bureau of Animal Industry Reports_, 1895-1896.

[56] _British Medical Journal_, 1895, vol. ii., p. 322.

[57] _British Medical Journal_, 1895, vol. ii., p. 322.

[58] _Journal of Comparative Pathology_, vol. x. (1897), pp.

150-189.

[59] E. W. Hope, M.D., D.Sc., _Report of the Health of

Liverpool during 1897_, p. 40.

[60] S. Rideal and A. G. R. Foulerton conclude, from a series

of experiments, that boric acid (1-2,000) and formaldehyde

(1-50,000) are effective preservatives for milk for a period

of twenty-four hours, and that these quantities have no

appreciable effect upon digestion or the digestibility of

foods preserved by them (_Public Health_, May, 1899, pp.

554-568).

[61] _Report from Wisconsin Agricultural Experiment Station_,

1896.

[62] Jenner Institute of Preventive Medicine (First Series

_Transactions_).

[63] _Centralblatt für Bakteriologie_, etc., II. Abteilung.

[64] _A Manual of Bacteriology, Clinical and Applied_, p. 397.

[65] Hewlett asserts that butter may contain from two to

forty-seven millions of bacteria per gram.

[66] Such pure cultures for such purposes are in the United

States termed "starters," because they start the process of

special ripening. For the sake of convenience the term will be

used here.

[67] The Essex County Council is one of the few public

bodies in England which have undertaken pioneer work in

this department of industry. Under the leadership of Mr.

David Houston, a course of elementary instruction in dairy

bacteriology as applied to modern dairy practice is given in

the County Biological Laboratory at Chelmsford.

[68] _Report of Storr's Agricultural Experiments Station,

State of Connecticut_, 1895.

[69] "Observations on Cheddar Cheese Making," _Reports of Bath

and West and Southern Counties Society_, 1898, pp. 163-171.

Mr. Lloyd's Reports to the West of England Society since

1892 contain various points respecting the application of

bacteriology to cheese-making.

[70] _Journal of Bath and West of England Society_, 1893,

1895, and 1897.

[71] _New York Medical Record_, 1894.

[72] _British Medical Journal_, 1896, ii., p. 760 _et seq._

[73] _Special Report of the Medical Officer to the Local

Government Board on Oyster Culture, etc._, 1896.

[74] Royal Commission on Tuberculosis, _Report_, 1895, pt. i.,

p. 13.

[75] _Ibid._, p. 18.

[76] _British Medical Journal_, 1895, vol. ii., p. 513.

[77] It should be distinctly understood that this table

is merely schematic and provisional. The details of toxin

production and its effect are still open to revision and

amendment.

[78] Sidney Martin, M.D., F.R.S., F.R.C.P., _Croonian Lectures

delivered before the Royal College of Physicians_, June, 1898.

[79] It is impossible here to enter into a detailed

consideration of the various views held with regard to the

formation of antitoxins. It is needless to remark that the

whole matter is one of abstruse technicality and intricacy.

These antitoxic bodies gradually increase in the blood and

tissues, and their action falls into two groups: (_a_)

_antitoxic_, which counteract the effects of the poison

itself; and (_b_) _antimicrobic_, which counteract the effects

of the bacillus itself. "In one and the same animal the blood

may contain a substance or substances which are both antitoxic

and antimicrobic, such, for example, as occurs in the process

of the formation of the diphtheria and tetanus antitoxic

serums" (Sidney Martin).

[80] Types of bodies possessing positive chemiotaxis for

bacteria are the salts of potassium, peptone, glycerine.

[81] Negative chemiotaxis is illustrated in alcohol, and free

acids, and alkalies.

[82] The friend of Addison and Pope, who married Mr.

Edward Wortley Montagu in 1712, and on his appointment to

the ambassadorship of the Porte in 1716 went with him to

Constantinople. They remained abroad for two years, during

which time Lady Wortley Montagu wrote her well-known Letters

to her sister the Countess of Mar, Pope, and others.

[83] Crookshank, _History and Pathology of Vaccination_.

[84] An exhaustive account of vaccine may be found in the

Milroy lectures delivered in 1898 at the Royal College of

Physicians by S. Monckton Copeman, M.D.

[85] Crookshank, _Bacteriology and Infective Diseases_;

Virchow, _The Huxley Lecture_, 1898.

[86] To shorten this period Dr. Cartwright Wood has adopted

a plan by which time may be saved, and 200 cc. injected say

within the first two or three weeks. This is accomplished by

using a "serum toxin" (containing albumoses, but not ferments)

previously to the broth toxin, an ingenious method which we

cannot enter into here.

[87] At the conclusion of the operation the cannula is removed

from the jugular vein, and the wound is closed by the valvular

character of the slit in the skin and vein and the elasticity

of the wall of the vein. No stitching or dressing is required.

Indeed, it is striking to observe in the horse an entire

absence of pain throughout the proceedings.

[88] The term _unit_ is used as a standard measurement. This

means the amount of antitoxin which will just neutralise ten

times the minimum fatal dose of the toxin in a guinea-pig

(250 grams toxin to kill on the fourth day). If 1 cc. of the

antitoxic serum is required for this, one unit is contained in

1 cc.; if 0.01 cc. is sufficient, then 100 units are contained

in the cc. Not less than 1500 units should be administered for

a dose, and repeated every twelve hours. In severe cases two

or three times this amount may be given.

[89] The value of antitoxin treatment in diphtheria is

discussed in the _Brit. Med. Jour._, 1899, pp. 197 and 268, by

E. W. Goodall, M.D.

[90] A detailed study of tuberculosis from its pathological

and bacteriological aspect will be found in _La Tuberculose

et son Bacille_, pt. i., Straus, Professeur à la Faculté de

Médecine de Paris.

[91] For differences of virulence between these conditions

of pulmonary tubercle see Lingard, _Local Government Board

Report_, 1888, p. 462.

[92] _Centralblatt. f. Bact. und Parasit._, vol. vii., p. 9.

[93] _Animal Tuberculosis_, p. 129.

[94] See the _Harben Lectures_, November, 1898, by Sir Richard

Thorne Thorne, Medical Officer to the Local Government Board;

also the _Report of the Royal Commission on Tuberculosis_,

1896-98.

[95] 1. Tuberculosis is a disease mainly affecting the lungs

(_consumption_, _decline_, _phthisis_) of young adults and the

bowels of infants (_tabes mesenterica_). It may affect any

part of the body, and its manifestations are very various. It

also affects animals, particularly cattle, by whom it may be

transmitted to man.

2. _Its direct cause_ is a microscopic vegetable cell, known

as the _Bacillus tuberculosis_, discovered by Koch in 1882.

This fungus requires to be magnified some hundreds of times

before it can even be seen. When it gains entrance to the

weakened body it sets up the disease, which is an _infectious_

disease, though different in degree to the infectiousness of,

say, measles.

3. _Trade influence and occupation_, in some cases,

undoubtedly predispose the individual to tubercle. Cramped

attitudes, exposure to dampness or cold, ill ventilation, and

exposure to inhalation of dust of various kinds, all act in

this way. In support of the evil effect of each of these four

conditions much evidence could he produced.

4. _Overcrowding_ has a definite influence in propagating

tubercular diseases. The agricultural counties without big

towns, like Worcestershire, Herefordshire, Buckinghamshire,

and Rutland, are the counties having the lowest mortality

from tuberculosis; whilst the crowded populations in

Northumberland, South Wales, Lancashire, London, and the

West Riding suffer most. Speaking more particularly, the

overcrowded areas of London, such as St. Giles', Strand,

Holborn, and Central London generally, show very high

tubercular death-rates.

5. _Tuberculosis is not increasing._ During the last thirty

years it has shown, with few exceptions, a steady decline

in all parts of England. "Consumption" is most fatal in

comparatively young people (fifteen to forty-five years),

whilst "tabes" and other forms of tubercle are fatal chiefly

to young children. These forms have not declined so much as

the lung form. The mortality in consumption of males has since

1866 been in excess of that of females. The age of maximum

fatality from consumption is _later_ than in the past, which

is probably due to improved hygiene and treatment.

6. _This decline has been due_, not to any special repressive

measures--for few or none have been carried out--but to a

general and extensive social improvement in the life of the

people, to an increase of knowledge respecting tuberculosis

and hygiene, to an enormous advance in sanitation, and to more

efficient land drainage.

7. _Not all persons are equally liable to consumption_, some

being much more susceptible than others. We have mentioned

the predisposing influence of certain trades. There is also

heredity, which acts, as we have said, in transmitting a

tubercular _tendency_, not commonly the actual virus of

the disease; there is, thirdly, the debilitating effect of

previous illness or chronic alcoholism; there is, fourthly,

the habitual breathing of rebreathed air; and, fifthly, there

are the conditions of the environment, like dampness and

darkness of the dwelling. Such influences as these weaken the

resisting power of the tissues, and thus afford a suitable

nidus for the bacillus conveyed in milk or by the inspiration

of infected dust.

8. _Consumption is curable_ if taken in time. In cases where

the lungs are half gone, and consist of large cavities, it is

obvious that curability is out of the question. But if the

disease can be properly treated in its earliest stages, there

is considerable likelihood of recovery.

9. _The breath is not dangerous_, as far as we know, but there

is danger from discharges of any kind from any infected part,

whether lungs or bowels; for such discharges, when dry, may

readily pollute the air, and either the bacilli or spores be

inhaled into the lungs.

10. _The chief channels of personal infection or the spread

of the disease amongst a community_ are two: (_a_) dried

tubercular sputum (or other tubercular discharges); (_b_)

infected milk or meat. So long as the former remains wet or

moist, infection cannot take place. It is, of course, better

to destroy it completely. As for milk and meat, boiling the

former and thoroughly cooking the latter will remove all

danger.

11. _The expectoration is infective._ This is one of the

commonest modes of infection, and to it is held to be due

the large amount of respiratory tuberculosis (consumption,

phthisis). The expectoration from the lungs must contain, from

the nature of the case, a very large number of bacilli. As

a matter of fact, a single consumptive individual can cough

up in a day millions of tubercle bacilli. When expectoration

becomes dry, the least current of air will disseminate the

infective dust, which can by that means be readily reinspired.

Expectoration on pavements and floors, as well as on

handkerchiefs, may thus become, on drying, a source of great

danger to others. The discharges from the bowels of infants

suffering from the disease also contain the infective material.

12. _Milk_, though a much more likely channel for conveyance

of tubercle than meat, is only or chiefly virulent when the

udder is the seat of tuberculous lesions. The consumption of

such milk is only dangerous when it contains a great number of

bacilli and is ingested in considerable quantity. Practically

the danger from using raw milk exists only for those persons

who use it as their sole or principal food, _e. g._, young

children. All danger is avoided by boiling or pasteurising the

milk.

At the same time there is an increasing amount of evidence

forthcoming at the present time which goes to prove that milk

is not infrequently tainted with tubercle (see p. 195). The

tuberculin test should be applied to all milch cows, and the

infected ones isolated from the herd. Milk supplies should be

more strictly inspected even than cowsheds.

13. There are several methods by which _meat infection can

be prevented_. In the first place, herds should be kept

healthy, and tubercular animals isolated. Cowsheds and byres

should be under sanitary supervision, especially as regards

overcrowding, dampness, lack of light, and uncleanliness.

Public slaughter-houses under a sanitary authority would

undoubtedly be most advantageous. Meat inspection should also

be more strictly attended to; efficient cooking, and avoidance

of "roll" meat which has not been thoroughly cooked in the

middle.

14. _Consumptive patients may diminish their disease._ Dr.

Arthur Ransome[95a] has laid down five axioms of hygiene for

phthisical patients which, if followed, would materially

improve the condition of such persons. At Davos, St. Moritz,

Nordrach and other places where they have been practised, the

beneficial change has been in many cases extraordinary:

(1) Abundance of light, nutritious, easily digested food,

which must comprise a large allowance of fat; small meals, but

frequent;

(2) An almost entirely open-air life, with as much sunshine as

can be obtained;

(3) Suitable clothing, mostly wool;

(4) Cleanliness and bracing cold-water treatment;

(5) Mild but regular exercise.

15. _Consumptive patients may also assist in preventing the

spread of the disease._ In the first place, they should

follow the hygienic directions just mentioned, because such

conditions fulfilled will materially lessen the contagiousness

of such patients; next, the expectoration must never be

allowed to get dry. A spitting-cup containing a little

disinfectant solution (one teaspoonful of strong carbolic acid

to two tablespoonfuls of water) should always be used, or the

expectoration received into paper handkerchiefs which can be

burnt. Spoons, forks, cups, and all such articles should be

thoroughly cleaned before being used by other persons. The

patient should not sleep in company with another, but occupy,

if possible, a separate bedroom.

Isolation hospitals for consumptives, as for patients

suffering from diphtheria, are now being established.

16. _House influence_ has some effect, both directly and

indirectly, upon tubercular diseases. Damp soils, darkness,

and small cubic space in the dwelling-house exert a very

prejudicial effect upon tubercular patients. Sir Richard

Thorne Thorne[95b] has described the favourable house for such

persons as one built upon a soil which is dry naturally or

freed by artificial means from the injurious influences of

dampness and of the oscillations of the underlying subsoil.

The house itself should be so constructed as to be protected

against dampness of site, foundations, and walls. Upon at

least two opposite sides of the dwelling-house there should be

enough open space to secure ample movement of air about it,

and free exposure to sunlight. Lastly, it should be possible

to have free movement of air by day and night through all

habitable rooms of the house. It is clear that many inhabited

houses could not stand to these tests; but effort should be

made to approach as near to such a standard as possible.

17. _Sunlight and fresh air_ are the greatest enemies to

infection.

18. _Disinfection is necessary after death from phthisis_,

and should be as complete as after any other infective

disease. Compulsory notification of fatal cases and compulsory

disinfection have been officially ordered by the Prussian

Government. In this country also absolute disinfection should

always be insisted upon after phthisis. Walls, floors,

carpets, curtains, etc., should be strictly sterilised.

Professor Delepine recommends spraying with 1-100 solution of

chloride of lime.

[95a] Arthur Ransome, M.D., F.R.S., _Treatment of Phthisis_.

[95b] _Practitioner_, vol. xlvi.

[96] _Journal of State Medicine_, vol. iv. (1896), p. 169.

[97] For a fuller statement see _Trans. Jenner Institute_

(First Series), pp. 7-32.

[98] See _Trans. Jenner Institute_ (First Series), A. G. R.

Foulerton, pp. 40-81.

[99] Dated 1890-91. The Commissioners were the late Beaven

Rake, M.D., G. A. Buckmaster, M.D., the late Professor

Kanthack, of Cambridge, the late Surgeon-Major Arthur Barclay,

and Surgeon-Major S. J. Thomson.

[100] _Bacteriology and Infective Diseases_ (1896), p. 144.

Professor Crookshank's Reports to the Agricultural Department

of the Privy Council constitute the most complete account of

this disease hitherto published.

[101] _Zeitschr. f. Hyg. und Inf. Krank._, xxv.

[102] _Journal of State Medicine_, December, 1897, p. 561.

[103] _Bacteriology and Infective Diseases_, p. 35.

[104] _British Medical Journal_, 1895 (February), p. 353.

[105] _British Medical Journal_, 1896 (August), p. 439.

[106] _Journal of State Medicine_, 1898 (November), p. 541.

[107] The measurement of cubic space is of course made by

multiplying together in feet the length, breadth, and height

of a room.

[108] _British Medical Journal_, 1898 (April), p. 1013.

INDEX

Abscess formation, 296-301

Acetous fermentation, 115, 127

Actinomycosis, 316

Aërobic organisms, 26

Agar, 21

Air, bacteriology of, 96-110

-- examination of, 96-99

-- of sewers, 105

-- expired, 102

-- bacteria and gravity, 106

-- standard of bacteria in, 108

-- pathogenic bacteria in, 109

-- passages, bacteria in, 103

Alcohol, formation of, 115

Alcoholic fermentation, 115, 117

Alexines, 249, 268

Alformant lamp for disinfection, 334

Algæ in water, 53

Ammoniacal fermentation, 115

Amylolytic ferments, 115

Anaërobic organisms, 132

-- methods of culture, 139-142

-- in hydrogen, 139, 140

-- in glucose-agar, 142

-- in Fränkel's tube, 140

-- in Buchner's tube, 141

Aniline dyes, 44

Antagonism of organisms, 33

Anthrax, 19, 26, 30, 34, 245

-- pathology of, 301

-- spores of, 302

-- bacillus of, 302

Antiseptics, 323, 332

-- definition of, 322

-- some of the chief, 332

Antitoxins, 245-250

-- preparation of, 259

-- use of, 263

-- unit of, 263

Appendix, 337

Arthrospores, 17

Artificial purification of water, 73

Ascospores, 120

Asiatic cholera, 65

Association of organisms, 31

Attenuation of virulence, 36

Bacillus, definition of, 11

-- aceti, 34, 129

-- acidi lactici, 131, 185, 190

-- amylobacter, 132

-- anthracis, 26, 31, 34, 110, 301-305

-- aquatilis, 53

-- butyricus, 133

-- coli communis, 32, 56, 58-62, 64, 67, 86, 88, 108, 151, 194, 237, 299,

315

-- cyanogenus, 193

-- diphtheriæ, 201, 212, 244, 289-296

-- enteriditis sporogenes, 60, 86, 87, 316

-- erythrosporus, 53

-- fluorescens liquefaciens, 43, 53, 64, 86

-- fluorescens non-liquefaciens, 53, 15

-- of cholera, 65-69

-- of diarrhœa, 203, 204

-- of influenza, 315

-- lactis erythrogenes, 193

-- lactis pituitosi, 193

-- lactis viscosus, 193

-- liquefaciens, 53, 151

-- of leprosy, 308-313

-- of glanders (mallei), 299, 319

-- mesentericus, 86, 151

-- mycoides, 151

-- of malignant œdema, 19, 172

-- No. 41, 219

-- pasteurianum, 130

-- of scarlet fever, 202

-- of symptomatic anthrax, 19, 171, 172

-- of plague, 306-308

Bacillus prodigiosus, 34, 151, 193, 238

-- pyocyaneus, 7, 34, 64, 110, 299

-- pyogenes fœtidus, 34

-- radicicola, 164

-- saponacei, 193

-- subtilis, 31, 86, 108

-- synxanthus, 194

-- of tetanus, 19, 168-171

-- termo, 53

-- of tubercle, 110, 212, 225, 274-291

-- typhosus, 41, 50, 55-62, 212

-- ubiquitous, 53

-- of yellow fever, 316

Bacteria, action of, 26

-- in sewage, 84

-- and wheat supply, 161

-- and fixation of nitrogen, 160-166

-- in cheese-making, 220-227

-- in the dairy, 215-227

-- products of, 240, 241

-- and disease, 264-321

-- the higher, 11, 33

-- in soil, 137-177

Bacterial action, 26

-- treatment of sewage, 90

Bacteroids, 166

Beer diseases, 134

Berkefeld filter, 52

Biogenesis, 3

Biology of bacteria, 1-36

Bitter fermentation, 191

Blood serum, 22

Blue milk, 193

Boracic acid, 205, 331

Bread, bacteria in, 238

Broth, 21

Brownian movement, 14

Bubonic plague, 306-308

Buchner's tube, 141

Butter, bacteria in, 213, 214

-- examination of, 214

-- bacterial flavouring of, 215

Butyric fermentation, 115, 132, 191

Carbol-fuchsin, 44

Carbol-gelatine, 62

Carbolic acid as a germicide, 332

Caries, dental, 104

Chamber, moist, 41

Channels of infection in disease, 269

-- in tubercle, 289

Cheese, bacteria in, 220

Chemical products of bacteria, 241

Chemical substances as disinfectants, 329

-- and bacteriological examination of water compared, 51

-- tests for nitrification, 158

Chemiotaxis, 15, 248

Chicken cholera, 320

Chinosol as a disinfectant, 336

Chloride of lime as a germicide, 331

Cholera, 65-68

-- diagnosis of, 68

-- and filtration, 75

-- and milk, 200

Chromogenic bacteria, 193, 241

Cladothrix, 8, 33

Clark's process, 73

Classification, 7

Coccus, definition of, 8

Colon bacillus, _see_ B. coli communis

Comma bacillus, 66

Commensalism, 162

Composition of bacteria, 12-14

Conditions affecting bacteria in water, 70

-- in milk, 186, 187

Contagion, 270

Corrosive sublimate as disinfectant, 331

Counter (Wolfhügel), 49

Cover-glass preparations, 44

Cream, bacteria in, 213

Crenothrix polyspora, 53

Creosol as a germicide, 332

Cultivation beds, 92

Culture media, 20

-- anaërobic, 139

-- hanging drop, 44

-- plate, 40-43

-- pure, 20, 46

-- shake, 62

Decomposition bacteria, 149

Denitrifying bacteria, 143, 149

Dental caries, 104

Deodorants, 323

Desiccation, 26

Diagnosis, 339

Diarrhœa of infants, 175, 316

Diphtheria, 243-245, 289-296

-- bacillus of, 289

-- toxins of, 244, 293

-- and milk supply, 201

-- and school influence, 294, 295

-- pseudo-bacillus of, 296

Diplococcus, definition of, 8

Diplococcus of gonorrhœa, 300

-- in pneumonia, 313

Directions for estimating disinfectants, etc., 324

Disease, production of, 264

Diseases of beer, 134

-- of plants, 35

-- of animals, 316-320

-- conveyed by water, 81

-- and soil, 173-177

Disinfectants, 322, 331

Disinfection, 322-336

-- of a room, 335

-- of walls, 335

-- of bedding, 335

-- of garments, 335

-- of excreta, 335

-- of wounds, 336

-- of hands, 336

Domestic purification of water, 79

Dunham's solution, 69

Dysentery, 319

Earth temperatures and disease, 175

Economic bacteria, 145

Egg cultures, 340

Elsner's medium, 62

Endospores, 17

Enteric fever, _see_ Typhoid

Enzymes, 114

Equifex disinfector, 328

-- sprayer, 334

Erysipelas, 299

Examination, bacteriological--

-- air, 96-99

-- cholera, 68

-- diphtheria, 290, 340

-- leprosy, 309

-- meat, 234

-- milk, 227

-- sewage, 80

-- soil, 138

-- tetanus, 170

-- tubercle, 276, 339

-- water, 43-48

-- yeasts, 119, _et seq._

Extracellular poisons, 244, 273

Fermentation, 111-136

-- acetous, 115, 127

-- alcoholic, 115, 117

-- ammoniacal, 115, _see_ under Soil

-- butyric, 115, 132, 191

-- lactic acid, 115, 130, 190

Ferments, organised, 114, 115

Ferments, unorganised, 114, 115

-- chromogenic, 193

-- curdling, 191

-- bitter, 191

-- slimy, 192

-- soapy, 193

Films, 123

Filter, domestic, 79

Filter-beds, 74

Filtration, milk, 206

-- method of air examination, 99

-- sand, 77-79

Fission, 16

Fixing specimens, 45

Flagella, 15

-- staining, 63

Food, bacteria in, 179, 180

Foot-and-mouth disease, 320

Formaldehyde and formalin, 205, 206, 333

Forms of bacteria, 8

Fränkel's tube, 140

-- pneumococcus, 314

Friedländer's pneumo-bacillus, 315

Gas, production of, 62, 241

Gathering-ground, 38

Gelatine, 21

-- carbol, 62

-- liquefaction of, 44

Gemmation, 119

Gentian-violet, aniline, 44

Germicidal temperatures, 30, 207

Germicides, 322, 331

Glanders, 319

Gonorrhœa, 300

Gram's method, 44, 338

Gravity, influence on bacteria, 106

Gypsum block, 121

Hæmatozoa, 320

Hanging drop cultivations, 44

Hansen's method of dilution, 123

Heat as steriliser, 30, 326

Heredity, 268, 269

Hesse's method of air examination, 98

Higher bacteria, 11

High yeasts, 125

Hot air steriliser, 31

Hydrogen cultivation, 139

Hydrophobia, treatment of, 253

Ice-cream, bacteria in, 236-238

-- examination of, 236

Immunity, 240-263

-- acquired, 247, 250

-- active, 250

-- artificial, 250

-- natural, 250

-- passive, 250

Incubation period, 271

Incubators, 22

Indol, formation of, 61

-- testing for, 61

Industries and bacteria, 135

Influenza, 315

Intracellular poisons, 34

Inversive ferments, 115

Involution forms, 12, 66

Kipp's apparatus for producing hydrogen, 27, 139

Klebs-Löffler bacillus, 289

Koch's plate method, 40

-- postulates, 266

-- comma bacillus, 66

-- bacillus of tubercle, 276

Lactic acid fermentation, 115, 130, 185, 190, 221, 226

Lactose, 190

Leguminosæ, fixation of nitrogen by, 163

Leprosy, 308-313

Leptothrix, 8, 33

Leuconostoc, 17

Light, influence upon bacteria, 24-26, 70

Liquefaction of gelatine, 44, 241

Low yeasts, 125

Lymph, glycerinated calf, 252

Lyon's, Washington, disinfector, 328

Maceration industries, 135

Malaria, 177, 320

Malignant œdema, 19, 172

Mallein, 319

Mastitis, 184

Measles, 321

Meat, 234

Media, culture, 20

Merismopedia, 11

Method of examination, 43-47

Metropolitan water supply, 72

Miasmatic diseases, 176

Micrococcus, definition of, 8

-- agilis, 16

-- aquatilis, 53

-- casei amari, 226

Micrococcus Freudenreichii, 192

-- gonorrhϾ, 299

-- tetragonus, 299

-- viscosus, 192

Milk, bacteriology of, 178-213

-- absorptivity of, 180

-- sources of pollution, 181-184

-- number of bacteria in, 185

-- influence of temperature upon, 186

-- influence of time of standing, 187

-- fermentation bacteria in, 189

-- constitution of, 189-195

-- disease-producing power of, 195

-- and tuberculosis, 197-199, 228, 290

-- and typhoid, 199

-- and cholera, 200

-- and diphtheria, 201

-- and scarlet fever, 202

-- and thrush, 203

-- methods of preservation of, 205

-- and added antiseptics, 205, 206

-- filtration of, 206

-- sterilisation of, 207

-- pasteurisation of, 208-213

-- products, bacteria in, 213-227

-- examination of, 227

-- and economic bacteria, 215-220

-- sterile, 181

-- kinds of bacteria in, 188

-- chromogenic, 193

-- cooling processes, 207, 209

Moist chamber, 41

Moisture necessary for bacteria, 23

Motility, 14

Moulds, 116

Mycoderma aceti, 127

Nasal passages, bacteria in, 103

Natural purification of water, 69

Needles, platinum, 22, 24

Nitrates, 147, 154

Nitric organism, 157, 158

Nitrification, 76, 143-159

-- chemistry of, 144-148

-- stages in, 145

-- bacteria of, 152

Nitrifying organisms, cultivation of, 156

Nitrogen, fixation of, 144, 160-168

Nitrous organism, 154, 158

Nodules on roots, bacteria in, 163

Oidium albicans, 203

Oxygen necessary for bacteria, 26

Oysters and bacteria, 229-234

Paraform for disinfection, 334

Parasitism, 27, 162

Parietti's method, 62

Pasteurisation of milk, 208-213

Pasteur's treatment of rabies, 253-258

Perlsucht, 283

Petri dishes, 50

Phagocytosis, 247

Phosphorescence, 26, 241

Pigment, formation of, 241

Place of bacteria in nature, 5

Plague, 306-308

Plant diseases, 35

Plate cultures, 40-46

Platinum needles, 22, 24

Pleomorphism, 12

Pneumo-bacillus, 315

Pneumococcus, 313

Pneumonia, 313

Polymorphism, 12

Postulates, Koch's, 266

Potato medium, 22

Pouchet's aëroscope, 96

Proteolytic ferments, 115

Proteus family, 86, 180, 297

-- vulgaris, 60, 86, 151, 194

-- zenkeri, 60

Pseudo-diphtheria bacillus, 296

Ptomaines, 179

Pure culture, 20, 46

Purification of water--

-- natural, 69

-- artificial, 73

Pus, 296

Putrefaction, 143-149

Pyocyanin, 299

Pyoxanthose, 299

Quantitative standard for water bacteria, 48, 49

-- air bacteria, 107

-- milk bacteria, 188

-- soil bacteria, 137

Quarter evil, 19, 171

Rabies, treatment of, 253

-- forms of, 253

-- pathology of, 254

-- results of treatment, 256

Reck's disinfector, 328

Reproduction of bacteria, methods of, 16

Retting, 135

Rinderpest, 320

Saccharomycetes, biology of, 119-121

-- methods of examination, 122

-- anomalous, 122

-- apiculatus, 127

-- aquifolii, 127

-- cerevisiæ, 117, 124, 126

-- conglomeratus, 126

-- ellipsoideus I., 126

-- ellipsoideus II., 126, 134

-- exiguus, 127

-- Hansenii, 127

-- illicis, 127

-- Ludwigii, 122

-- mycoderma, 127

-- pastorianus I., 127, 134

-- pastorianus II., 127

-- pastorianus III., 127, 134

-- pyriformis, 127

Salicylic acid as antiseptic, 205, 206

Saprophytes, 27, 166

Sarcina, 10

Scarlet fever, 202, 321

Sedgwick's method of air analysis, 99

Sedimentation, 71, 73

Septic processes, 296

-- tank, 90

Sewage, organisms in, 84

-- bacterial treatment of, 89

Sewer air, 87

-- and toxicity of bacteria, 105

Shake culture, 62

Shell-fish and bacteria, 229, 234

Small-pox, 251, 321

Soil, bacteriology of, 137

-- examination of, 138

-- kinds of bacteria in, 142-145

-- and its relation to disease, 173, 176, 177

Species of bacteria, 29

Spirillum, definition of, 11

-- of cholera, 66

Spontaneous generation, 2

Spores, kinds of, 17-19

-- resistance of, 19, 278

-- staining of, 19

-- of yeasts, 122

Staining methods, 45

Staphylococcus, 10, 296

-- cereus albus, 297

-- pyogenes aureus, 88, 108, 297

Steam as a disinfector, 326

-- disinfectors, 327-329

-- steriliser, 326

-- saturated, 327

-- superheated, 327

Steam current, 327

Sterilisation, 29-31

-- methods of, 30, 31

Streptococcus, 9, 297

-- pyogenes, 299

-- Hollandicus, 192

Streptothrix, 317

Structure of bacteria, 8

Sulphurous acid as a germicide, 332

Suppuration, 296-301

Swine fever, 320

Symbiosis, 162

Symptomatic anthrax, 171

Table of economic bacteria in soil, 145

Temperature, influence of, on bacteria, 23

Tetanus, 19, 168, 245

-- toxin of, 168

Thresh's disinfector, 328

Thrush, 203

Tissues, effect of, on bacteria, 267

Tobacco-curing, 136

Toxins, 28, 241-247, 272

Tuberculin, 281

Tuberculosis, 274-292

-- pathology of, 274

-- varieties of, 275

-- history of, 276

-- conveyed by the air, 104

-- and the milk supply, 196-198, 290

-- giant cells in, 275

-- bacillus of, 276

-- cultivation of bacillus of, 277

-- spores of, 277

-- relation of bacillus to disease, 279

-- toxins of, 281

-- of animals, 283

-- prevention of, 286-292

-- disinfection in cases of, 292

-- decline of, 288

-- and overcrowding, 288

-- channels of infection in, 289

-- expectoration in, 290

Tuberculosis and house influence, 291

-- and glanders, 319

Typhoid fever, 56

-- bacillus of, 55-58

-- micro-pathology, 57

-- bacillus compared with B. coli, 58

-- bacillus in sewage, 59

-- bacillus in drinking water, 60

-- tests for bacillus of, 61-64

-- and soil, 173, 176

-- conveyed by the air, 105

-- and milk supply, 199

Tyrotoxicon, 205, 237

Unit of antitoxin, 263

Urea, 148

Vaccination, 251-253

Vaccines, plague, 257, 259

-- cholera, 257

-- small-pox, 251

Vaccinia, 251

Variolation, 250, 251

Virulence increased, 32

-- diminished, 36

Water, bacteria in, 37-84

-- number of bacteria in, 38

-- examination of, 39-52

-- disease organisms found in, 55

-- natural purification of, 69

-- artificial purification of, 73

-- filtration of, 74

-- domestic purification of, 79

-- pollution of, 82

Wheat supply and bacteria, 161

Widal reaction, 63, 340

Wooden tongue, 318

Wool-sorters' disease, 305

Yeasts, 116

Yellow fever, 316

Ziehl-Neelsen stain, 44, 340

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