Manual of Surgery/Chapter II

CHAPTER II

CONDITIONS WHICH INTERFERE WITH REPAIR

SURGICAL BACTERIOLOGY

Want of rest--Irritation--Unhealthy tissues--Pathogenic bacteria. SURGICAL BACTERIOLOGY--General characters of   bacteria--Classification of bacteria--Conditions of bacterial life--Pathogenic powers of bacteria--Results of bacterial growth--Death of bacteria--Immunity--Antitoxic sera--Identification of bacteria--Pyogenic bacteria.

In the management of wounds and other surgical conditions it is necessary to eliminate various extraneous influences which tend to delay or arrest the natural process of repair.

Of these, one of the most important is undue movement of the affected part. "The first and great requisite for the restoration of injured parts is _rest_," said John Hunter; and physiological and mechanical rest as the chief of natural therapeutic agents was the theme of John Hilton's classical work--_Rest and Pain_. In this connection it must be understood that "rest" implies more than the mere state of physical repose: all physiological as well as mechanical function must be prevented as far as is possible. For instance, the constituent bones of a joint affected with tuberculosis must be controlled by splints or other appliances so that no movement can take place between them, and the limb may not be used for any purpose; physiological rest may be secured to an inflamed colon by making an artificial anus in the caecum; the activity of a diseased kidney may be diminished by regulating the quantity and quality of the fluids taken by the patient.

Another source of interference with repair in wounds is _irritation_, either by mechanical agents such as rough, unsuitable dressings, bandages, or ill-fitting splints; or by chemical agents in the form of strong lotions or other applications.

An _unhealthy or devitalised condition of the patient's tissues_ also hinders the reparative process. Bruised or lacerated skin heals less kindly than skin cut with a smooth, sharp instrument; and persistent venous congestion of a part, such as occurs, for example, in the leg when the veins are varicose, by preventing the access of healthy blood, tends to delay the healing of open wounds. The existence of grave constitutional disease, such as Bright's disease, diabetes, syphilis, scurvy, or alcoholism, also impedes healing.

Infection by disease-producing micro-organisms or _pathogenic bacteria_ is, however, the most potent factor in disturbing the natural process of repair in wounds.

SURGICAL BACTERIOLOGY

The influence of micro-organisms in the causation of disease, and the role played by them in interfering with the natural process of repair, are so important that the science of applied bacteriology has now come to dominate every department of surgery, and it is from the standpoint of bacteriology that nearly all surgical questions have to be considered.

The term _sepsis_ as now used in clinical surgery no longer retains its original meaning as synonymous with "putrefaction," but is employed to denote all conditions in which bacterial infection has taken place, and more particularly those in which pyogenic bacteria are present. In the same way the term _aseptic_ conveys the idea of freedom from all forms of bacteria, putrefactive or otherwise; and the term _antiseptic_ is used to denote a power of counteracting bacteria and their products.

granular mass of protoplasm, enclosed in a thin gelatinous envelope. Many forms are motile--some in virtue of fine thread-like flagella, and others through contractility of the protoplasm. The great majority multiply by simple fission, each parent cell giving rise to two daughter cells, and this process goes on with extraordinary rapidity. Other varieties, particularly bacilli, are propagated by the formation of _spores_. A spore is a minute mass of protoplasm surrounded by a dense, tough membrane, developed in the interior of the parent cell. Spores are remarkable for their tenacity of life, and for the resistance they offer to the action of heat and chemical germicides.
 * 1) General Characters of Bacteria.#--A _bacterium_ consists of a finely

Bacteria are most conveniently classified according to their shape. Thus we recognise (1) those that are globular--_cocci_; (2) those that resemble a rod--_bacilli_; (3) the spiral or wavy forms--_spirilla_.

_Cocci_ or _micrococci_ are minute round bodies, averaging about 1 [micron] in diameter. The great majority are non-motile. They multiply by fission; and when they divide in such a way that the resulting cells remain in pairs, are called _diplococci_, of which the bacteria of gonorrhoea and pneumonia are examples (Fig. 5). When they divide irregularly, and form grape-like bunches, they are known as _staphylococci_, and to this variety the commonest pyogenic or pus-forming organisms belong (Fig. 2). When division takes place only in one axis, so that long chains are formed, the term _streptococcus_ is applied (Fig. 3). Streptococci are met with in erysipelas and various other inflammatory and suppurative processes of a spreading character.

_Bacilli_ are rod-shaped bacteria, usually at least twice as long as they are broad (Fig. 4). Some multiply by fission, others by sporulation. Some forms are motile, others are non-motile. Tuberculosis, tetanus, anthrax, and many other surgical diseases are due to different forms of bacilli.

_Spirilla_ are long, slender, thread-like cells, more or less spiral or wavy. Some move by a screw-like contraction of the protoplasm, some by flagellae. The spirochaete associated with syphilis (Fig. 36) is the most important member of this group.

development a suitable food-supply in the form of proteins, carbohydrates, and salts of calcium and potassium which they break up into simpler elements. An alkaline medium favours bacterial growth; and moisture is a necessary condition; spores, however, can survive the want of water for much longer periods than fully developed bacteria. The necessity for oxygen varies in different species. Those that require oxygen are known as _aerobic bacilli_ or _aerobes_; those that cannot live in the presence of oxygen are spoken of as _anaerobes_. The great majority of bacteria, however, while they prefer to have oxygen, are able to live without it, and are called _facultative anaerobes_.
 * 1) Conditions of Bacterial Life.#--Bacteria require for their growth and

The most suitable temperature for bacterial life is from 95 to 102 F., roughly that of the human body. Extreme or prolonged cold paralyses but does not kill micro-organisms. Few, however, survive being raised to a temperature of 134.5 F. Boiling for ten to twenty minutes will kill all bacteria, and the great majority of spores. Steam applied in an autoclave under a pressure of two atmospheres destroys even the most resistant spores in a few minutes. Direct sunlight, electric light, or even diffuse daylight, is inimical to the growth of bacteria, as are also Rontgen rays and radium emanations.

pathogenic bacteria--that is, bacteria capable of producing disease in the human subject. This capacity depends upon two sets of factors--(1) certain features peculiar to the invading bacteria, and (2) others peculiar to the host. Many bacteria have only the power of living upon dead matter, and are known as _saphrophytes_. Such as do nourish in living tissue are, by distinction, known as _parasites_. The power a given parasitic micro-organism has of multiplying in the body and giving rise to disease is spoken of as its _virulence_, and this varies not only with different species, but in the same species at different times and under varying circumstances. The actual number of organisms introduced is also an important factor in determining their pathogenic power. Healthy tissues can resist the invasion of a certain number of bacteria of a given species, but when that number is exceeded, the organisms get the upper hand and disease results. When the organisms gain access directly to the blood-stream, as a rule they produce their effects more certainly and with greater intensity than when they are introduced into the tissues.
 * 1) Pathogenic Properties of Bacteria.#--We are now only concerned with

Further, the virulence of an organism is modified by the condition of the patient into whose tissues it is introduced. So long as a person is in good health, the tissues are able to resist the attacks of moderate numbers of most bacteria. Any lowering of the vitality of the individual, however, either locally or generally, at once renders him more susceptible to infection. Thus bruised or torn tissue is much more liable to infection with pus-producing organisms than tissues clean-cut with a knife; also, after certain diseases, the liability to infection by the organisms of diphtheria, pneumonia, or erysipelas is much increased. Even such slight depression of vitality as results from bodily fatigue, or exposure to cold and damp, may be sufficient to turn the scale in the battle between the tissues and the bacteria. Age is an important factor in regard to the action of certain bacteria. Young subjects are attacked by diphtheria, tuberculosis, acute osteomyelitis, and some other diseases with greater frequency and severity than those of more advanced years.

In different races, localities, environment, and seasons, the pathogenic powers of certain organisms, such as those of erysipelas, diphtheria, and acute osteomyelitis, vary considerably.

There is evidence that a _mixed infection_--that is, the introduction of more than one species of organism, for example, the tubercle bacillus and a pyogenic staphylococcus--increases the severity of the resulting disease. If one of the varieties gain the ascendancy, the poisons produced by the others so devitalise the tissue cells, and diminish their power of resistance, that the virulence of the most active organisms is increased. On the other hand, there is reason to believe that the products of certain organisms antagonise one another--for example, an attack of erysipelas may effect the cure of a patch of tuberculous lupus.

Lastly, in patients suffering from chronic wasting diseases, bacteria may invade the internal organs by the blood-stream in enormous numbers and with great rapidity, during the period of extreme debility which shortly precedes death. The discovery of such collections of organisms on post-mortem examination may lead to erroneous conclusions being drawn as to the cause of death.

and erysipelas, and certain of the pyogenic bacteria, show little tendency to pass far beyond the point at which they gain an entrance to the body. Others, on the contrary--for example, the tubercle bacillus and the organism of acute osteomyelitis--although frequently remaining localised at the seat of inoculation, tend to pass to distant parts, lodging in the capillaries of joints, bones, kidney, or lungs, and there producing their deleterious effects.
 * 1) Results of Bacterial Growth.#--Some organisms, such as those of tetanus

In the human subject, multiplication in the blood-stream does not occur to any great extent. In some general acute pyogenic infections, such as osteomyelitis, cellulitis, etc., pure cultures of staphylococci or of streptococci may be obtained from the blood. In pneumococcal and typhoid infections, also, the organisms may be found in the blood.

It is by the vital changes they bring about in the parts where they settle that micro-organisms disturb the health of the patient. In deriving nourishment from the complex organic compounds in which they nourish, the organisms evolve, probably by means of a ferment, certain chemical products of unknown composition, but probably colloidal in nature, and known as _toxins_. When these poisons are absorbed into the general circulation they give rise to certain groups of symptoms--such as rise of temperature, associated circulatory and respiratory derangements, interference with the gastro-intestinal functions and also with those of the nervous system--which go to make up the condition known as blood-poisoning, toxaemia, or _bacterial intoxication_. In addition to this, certain bacteria produce toxins that give rise to definite and distinct groups of symptoms--such as the convulsions of tetanus, or the paralyses that follow diphtheria.

_Death of Bacteria._--Under certain circumstances, it would appear that the accumulation of the toxic products of bacterial action tends to interfere with the continued life and growth of the organisms themselves, and in this way the natural cure of certain diseases is brought about. Outside the body, bacteria may be killed by starvation, by want of moisture, by being subjected to high temperature, or by the action of certain chemical agents of which carbolic acid, the perchloride and biniodide of mercury, and various chlorine preparations are the most powerful.

diseases, from which they are said to enjoy a _natural immunity_. In many acute diseases one attack protects the patient, for a time at least, from a second attack--_acquired immunity_.
 * 1) Immunity.#--Some persons are insusceptible to infection by certain

_Phagocytosis._--In the production of immunity the leucocytes and certain other cells play an important part in virtue of the power they possess of ingesting bacteria and of destroying them by a process of intra-cellular digestion. To this process Metchnikoff gave the name of _phagocytosis_, and he recognised two forms of _phagocytes_: (1) the _microphages_, which are the polymorpho-nuclear leucocytes of the blood; and (2) the _macrophages_, which include the larger hyaline leucocytes, endothelial cells, and connective-tissue corpuscles.

During the process of phagocytosis, the polymorpho-nuclear leucocytes in the circulating blood increase greatly in numbers (_leucocytosis_), as well as in their phagocytic action, and in the course of destroying the bacteria they produce certain ferments which enter the blood serum. These are known as _opsonins_ or _alexins_, and they act on the bacteria by a process comparable to narcotisation, and render them an easy prey for the phagocytes.

_Artificial or Passive Immunity._--A form of immunity can be induced by the introduction of protective substances obtained from an animal which has been actively immunised. The process by which passive immunity is acquired depends upon the fact that as a result of the reaction between the specific virus of a particular disease (the _antigen_) and the tissues of the animal attacked, certain substances--_antibodies_--are produced, which when transferred to the body of a susceptible animal protect it against that disease. The most important of these antibodies are the _antitoxins_. From the study of the processes by which immunity is secured against the effects of bacterial action the serum and vaccine methods of treating certain infective diseases have been evolved. The _serum treatment_ is designed to furnish the patient with a sufficiency of antibodies to neutralise the infection. The anti-diphtheritic and the anti-tetanic act by neutralising the specific toxins of the disease--_antitoxic serums_; the anti-streptcoccic and the serum for anthrax act upon the bacteria--_anti-bacterial serums_.

A _polyvalent_ serum, that is, one derived from an animal which has been immunised by numerous strains of the organism derived from various sources, is much more efficacious than when a single strain has been used.

_Clinical Use of Serums._--Every precaution must be taken to prevent organismal contamination of the serum or of the apparatus by means of which it is injected. Syringes are so made that they can be sterilised by boiling. The best situations for injection are under the skin of the abdomen, the thorax, or the buttock, and the skin should be purified at the seat of puncture. If the bulk of the full dose is large, it should be divided and injected into different parts of the body, not more than 20 c.c. being injected at one place. The serum may be introduced directly into a vein, or into the spinal canal, _e.g._ anti-tetanic serum. The immunity produced by injections of antitoxic sera lasts only for a comparatively short time, seldom longer than a few weeks.

_"Serum Disease" and Anaphylaxis._--It is to be borne in mind that some patients exhibit a supersensitiveness with regard to protective sera, an injection being followed in a few days by the appearance of an urticarial or erythematous rash, pain and swelling of the joints, and a variable degree of fever. These symptoms, to which the name _serum disease_ is applied, usually disappear in the course of a few days.

The term _anaphylaxis_ is applied to an allied condition of supersensitiveness which appears to be induced by the injection of certain substances, including toxins and sera, that are capable of acting as antigens. When a second injection is given after an interval of some days, if anaphylaxis has been established by the first dose, the patient suddenly manifests toxic symptoms of the nature of profound shock which may even prove fatal. The conditions which render a person liable to develop anaphylaxis and the mechanism by which it is established are as yet imperfectly understood.

_Vaccine Treatment._--The vaccine treatment elaborated by A. E. Wright consists in injecting, while the disease is still active, specially prepared dead cultures of the causative organisms, and is based on the fact that these "vaccines" render the bacteria in the tissues less able to resist the attacks of the phagocytes. The method is most successful when the vaccine is prepared from organisms isolated from the patient himself, _autogenous vaccine_, but when this is impracticable, or takes a considerable time, laboratory-prepared polyvalent _stock vaccines_ may be used.

_Clinical Use of Vaccines._--Vaccines should not be given while a patient is in a negative phase, as a certain amount of the opsonin in the blood is used up in neutralising the substances injected, and this may reduce the opsonic index to such an extent that the vaccines themselves become dangerous. As a rule, the propriety of using a vaccine can be determined from the general condition of the patient. The initial dose should always be a small one, particularly if the disease is acute, and the subsequent dosage will be regulated by the effect produced. If marked constitutional disturbance with rise of temperature follows the use of a vaccine, it indicates a negative phase, and calls for a diminution in the next dose. If, on the other hand, the local as well as the general condition of the patient improves after the injection, it indicates a positive phase, and the original dose may be repeated or even increased. Vaccines are best introduced subcutaneously, a part being selected which is not liable to pressure, as there is sometimes considerable local reaction. Repeated doses may be necessary at intervals of a few days.

The vaccine treatment has been successfully employed in various tuberculous lesions, in pyogenic infections such as acne, boils, sycosis, streptococcal, pneumococcal, and gonococcal conditions, in infections of the accessory air sinuses, and in other diseases caused by bacteria.

PYOGENIC BACTERIA

From the point of view of the surgeon the most important varieties of micro-organisms are those that cause inflammation and suppuration--the _pyogenic bacteria_. This group includes a great many species, and these are so widely distributed that they are to be met with under all conditions of everyday life.

The nature of the inflammatory and suppurative processes will be considered in detail later; suffice it here to say that they are brought about by the action of one or other of the organisms that we have now to consider.

It is found that the _staphylococci_, which cluster into groups, tend to produce localised lesions; while the chain-forms--_streptococci_--give rise to diffuse, spreading conditions. Many varieties of pyogenic bacteria have now been differentiated, the best known being the staphylococcus aureus, the streptococcus, and the bacillus coli communis.

[Illustration: FIG. 2.--Staphylococcus aureus in Pus from case of Osteomyelitis. x 1000 diam. Gram's stain.]

_Staphylococcus Aureus._--This is the commonest organism found in localised inflammatory and suppurative conditions. It varies greatly in its virulence, and is found in such widely different conditions as skin pustules, boils, carbuncles, and some acute inflammations of bone. As seen by the microscope it occurs in grape-like clusters, fission of the individual cells taking place irregularly (Fig. 2). When grown in artificial media, the colonies assume an orange-yellow colour--hence the name _aureus_. It is of high vitality and resists more prolonged exposure to high temperatures than most non-sporing bacteria. It is capable of lying latent in the tissues for long periods, for example, in the marrow of long bones, and of again becoming active and causing a fresh outbreak of suppuration. This organism is widely distributed: it is found on the skin, in the mouth, and in other situations in the body, and as it is present in the dust of the air and on all objects upon which dust has settled, it is a continual source of infection unless means are taken to exclude it from wounds.

The _staphylococcus albus_ is much less common than the aureus, but has the same properties and characters, save that its growth on artificial media assumes a white colour. It is the common cause of stitch abscesses, the skin being its normal habitat.

[Illustration: FIG. 3.--Streptococci in Pus from an acute abscess in subcutaneous tissue. x 1000 diam. Gram's stain.]

_Streptococcus Pyogenes._--This organism also varies greatly in its virulence; in some instances--for example in erysipelas--it causes a sharp attack of acute spreading inflammation, which soon subsides without showing any tendency to end in suppuration; under other conditions it gives rise to a generalised infection which rapidly proves fatal. The streptococcus has less capacity of liquefying the tissues than the staphylococcus, so that pus formation takes place more slowly. At the same time its products are very potent in destroying the tissues in their vicinity, and so interfering with the exudation of leucocytes which would otherwise exercise their protective influence. Streptococci invade the lymph spaces, and are associated with acute spreading conditions such as phlegmonous or erysipelatous inflammations and suppurations, lymphangitis and suppuration in lymph glands, and inflammation of serous and synovial membranes, also with a form of pneumonia which is prone to follow on severe operations in the mouth and throat. Streptococci are also concerned in the production of spreading gangrene and pyaemia.

Division takes place in one axis, so that chains of varying length are formed (Fig. 3). It is less easily cultivated by artificial media than the staphylococcus; it forms a whitish growth.

[Illustration: FIG. 4.--Bacillus coli communis in Urine, from a case of Cystitis. x 1000 diam. Leishman's stain.]

_Bacillus Coli Communis._--This organism, which is a normal inhabitant of the intestinal tract, shows a great tendency to invade any organ or tissue whose vitality is lowered. It is causatively associated with such conditions as peritonitis and peritoneal suppuration resulting from strangulated hernia, appendicitis, or perforation in any part of the alimentary canal. In cystitis, pyelitis, abscess of the kidney, suppuration in the bile-ducts or liver, and in many other abdominal conditions, it plays a most important part. The discharge from wounds infected by this organism has usually a foetid, or even a faecal odour, and often contains gases resulting from putrefaction.

It is a small rod-shaped organism with short flagellae, which render it motile (Fig. 4). It closely resembles the typhoid bacillus, but is distinguished from it by its behaviour in artificial culture media.

[Illustration: FIG. 5.--Fraenkel's Pneumococci in Pus from Empyema following Pneumonia. x 100 diam. Stained with Muir's capsule stain.]

_Pneumo-bacteria._--Two forms of organism associated with pneumonia--_Fraenkel's pneumococcus_ (one of the diplococci) (Fig. 5) and _Friedlander's pneumo-bacillus_ (a short rod-shaped form)--are frequently met with in inflammations of the serous and synovial membranes, in suppuration in the liver, and in various other inflammatory and suppurative conditions.

_Bacillus Typhosus._--This organism has been found in pure culture in suppurative conditions of bone, of cellular tissue, and of internal organs, especially during convalescence from typhoid fever. Like the staphylococcus, it is capable of lying latent in the tissues for long periods.

_Other Pyogenic Bacteria._--It is not necessary to do more than name some of the other organisms that are known to be pyogenic, such as the bacillus pyocyaneus, which is found in green and blue pus, the micrococcus tetragenus, the gonococcus, actinomyces, the glanders bacillus, and the tubercle bacillus. Most of these will receive further mention in connection with the diseases to which they give rise.

pathological conditions, are associated with an increase in the number of leucocytes in the blood throughout the circulatory system. This condition of the blood, which is known as _leucocytosis_, is believed to be due to an excessive output and rapid formation of leucocytes by the bone marrow, and it probably has as its object the arrest and destruction of the invading organisms or toxins. To increase the resisting power of the system to pathogenic organisms, an artificial leucocytosis may be induced by subcutaneous injection of a solution of nucleinate of soda (16 minims of a 5 per cent. solution).
 * 1) Leucocytosis.#--Most bacterial diseases, as well as certain other

The _normal_ number of leucocytes per cubic millimetre varies in different individuals, and in the same individual under different conditions, from 5000 to 10,000: 7500 is a normal average, and anything above 12,000 is considered abnormal. When leucocytosis is present, the number may range from 12,000 to 30,000 or even higher; 40,000 is looked upon as a high degree of leucocytosis. According to Ehrlich, the following may be taken as the standard proportion of the various forms of leucocytes in normal blood: polynuclear neutrophile leucocytes, 70 to 72 per cent.; lymphocytes, 22 to 25 per cent.; eosinophile cells, 2 to 4 per cent.; large mononuclear and transitional leucocytes, 2 to 4 per cent.; mast-cells, 0.5 to 2 per cent.

In estimating the clinical importance of a leucocytosis, it is not sufficient merely to count the aggregate number of leucocytes present. A differential count must be made to determine which variety of cells is in excess. In the majority of surgical affections it is chiefly the granular polymorpho-nuclear neutrophile leucocytes that are in excess (_ordinary leucocytosis_). In some cases, and particularly in parasitic diseases such as trichiniasis and hydatid disease, the eosinophile leucocytes also show a proportionate increase (_eosinophilia_). The term _lymphocytosis_ is applied when there is an increase in the number of circulating lymphocytes, as occurs, for example, in lymphatic leucaemia, and in certain cases of syphilis.

Leucocytosis is met with in nearly all acute infective diseases, and in acute pyogenic inflammatory affections, particularly in those attended with suppuration. In exceptionally acute septic conditions the extreme virulence of the toxins may prevent the leucocytes reacting, and leucocytosis may be absent. The absence of leucocytosis in a disease in which it is usually present is therefore to be looked upon as a grave omen, particularly when the general symptoms are severe. In some cases of malignant disease the number of leucocytes is increased to 15,000 or 20,000. A few hours after a severe haemorrhage also there is usually a leucocytosis of from 15,000 to 30,000, which lasts for three or four days (Lyon). In cases of haemorrhage the leucocytosis is increased by infusion of fluids into the circulation. After all operations there is at least a transient leucocytosis (_post-operative leucocytosis_) (F. I. Dawson).

The leucocytosis begins soon after the infection manifests itself--for example, by shivering, rigor, or rise of temperature. The number of leucocytes rises somewhat rapidly, increases while the condition is progressing, and remains high during the febrile period, but there is no constant correspondence between the number of leucocytes and the height of the temperature. The arrest of the inflammation and its resolution are accompanied by a fall in the number of leucocytes, while the occurrence of suppuration is attended with a further increase in their number.

In interpreting the "blood count," it is to be kept in mind that a _physiological leucocytosis_ occurs within three or four hours of taking a meal, especially one rich in proteins, from 1500 to 2000 being added to the normal number. In this _digestion leucocytosis_ the increase is chiefly in the polynuclear neutrophile leucocytes. Immediately before and after delivery, particularly in primiparae, there is usually a moderate degree of leucocytosis. If the labour is normal and the puerperium uncomplicated, the number of leucocytes regains the normal in about a week. Lactation has no appreciable effect on the number of leucocytes. In new-born infants the leucocyte count is abnormally high, ranging from 15,000 to 20,000. In children under one year of age, the normal average is from 10,000 to 20,000.

_Absence of Leucocytosis--Leucopenia._--In certain infective diseases the number of leucocytes in the circulating blood is abnormally low--3000 or 4000--and this condition is known as _leucopenia_. It occurs in typhoid fever, especially in the later stages of the disease, in tuberculous lesions unaccompanied by suppuration, in malaria, and in most cases of uncomplicated influenza. The occurrence of leucocytosis in any of these conditions is to be looked upon as an indication that a mixed infection has taken place, and that some suppurative process is present.

The absence of leucocytosis in some cases of virulent septic poisoning has already been referred to.

It will be evident that too much reliance must not be placed upon a single observation, particularly in emergency cases. Whenever possible, a series of observations should be made, the blood being examined about four hours after meals, and about the same hour each day.

The clinical significance of the blood count in individual diseases will be further referred to.

_The Iodine or Glycogen Reaction._--The leucocyte count may be supplemented by staining films of the blood with a watery solution of iodine and potassium iodide. In all advancing purulent conditions, in septic poisonings, in pneumonia, and in cancerous growths associated with ulceration, a certain number of the polynuclear leucocytes are stained a brown or reddish-brown colour, due to the action of the iodine on some substance in the cells of the nature of glycogen. This reaction is absent in serous effusions, in unmixed tuberculous infections, in uncomplicated typhoid fever, and in the early stages of cancerous growths.