Part 6

The heat of inflammation is one of the most important clinical features, yet not indispensable, as appears from its absence in chronic interstitial forms of inflammation. In the acute varieties of inflammation an elevated temperature is constant, and its observation and record furnish a most valuable means of determining the beginning and progress of an inflammation, which, for a time, may furnish but little additional evidence.

The heat of inflammation is the prominent characteristic of inflammatory fever, and it is the study of this variety of fever of late years which has resulted in an intelligible and relatively satisfactory theory concerning fevers in general. Information of much value is to be found in the recent work of Wood, which contains abundant historical information, as well as extensive original observations and conclusions.

Inflammatory fevers are distinguished from idiopathic forms. The latter variety includes the occurrence of fever as an attribute of the disease concerned, the more characteristic symptoms of which follow the febrile outbreak. Local inflammatory processes may take place during the progress of the disease with its fever, but such processes are co-effects of the cause of the latter, rather than its cause. Most of those diseases in which fever occurs as one of the joint effects of the cause of the disease, are included among the infective or zymotic classes.

The inflammatory fevers are those attending an acute inflammatory process, and are secondary to, and occasioned by, the latter. The type of this variety is seen in the fever occurring during the progress of a wound, whether its course is toward healing or extension. Such {38} traumatic fevers are characterized as septic or aseptic; the former including the conditions of septicæmia and pyæmia. The aseptic traumatic fevers, as described by Volkmann, are those which pursue their course with an elevated temperature, but without most of the other febrile phenomena.

Fever in general is characterized by a combination of disturbances in the physiological processes of the body. Such processes are those concerned in the production and dissipation of heat, in respiration and circulation, digestion and secretion, and in mental, motor, and other sensorial action. Such disturbances are manifested by a persistent elevation of temperature, an increased destruction of tissue, a quickened and modified pulse, accelerated breathing, increased thirst, diminished appetite, and diminished quantity and altered quality of the secretions. The sensorial disturbances include wakefulness and stupor, headache, delirium, twitchings, cramps, and other symptoms indicative of functional impairment of the nervous system.

Of all these manifold evidences of fever, the elevation of temperature is the one whose cause, range, and results have been most carefully and critically investigated. No record of a case in which fever is present is regarded as complete without the chart of the daily variations in temperature, respiration, and circulation. The practical value of such records is thus admitted, and in the experiments relating to the origin of animal heat the observations of temperature are as essential as the chemical analyses, each of which supplements the other.

The more accurate determination of the heat produced in the body is obtained either by the use of the calorimeter (an apparatus for measuring the collected heat liberated from the body) or by estimating the quantity of heat produced in the destruction of the constituents of the body from quantitative analyses of the discharged carbonic acid and urea. The results of such investigations are regarded by Rosenthal as possessing only a relative value, but justify the conclusion that most of the heat produced in the organism results from the oxidation of its constituents.

For the preservation of health it is essential that this heat should be removed from the body in such quantity that the temperature of the latter shall not vary to any considerable extent, for any considerable time, from 37.2° C. (98.4° F.). The removal of the heat is mainly accomplished by its radiation or conduction into a surrounding cooler medium, and by the evaporation of moisture from the surface of the body. Too great a removal of heat results in death from freezing, while too great an accumulation of heat terminates fatally from the effects of an unduly elevated temperature. To ensure the normal range of temperature, constantly changing relations must exist between the production of heat and its dissipation. The cooler the surroundings, the more must heat be produced, or the less must heat be evolved from the body.

An increased production of heat is obvious under conditions of climate demanding prolonged exposure to low temperature. An abundantly fatty diet promotes the formation of heat, while suitable clothing checks its dissipation. Although it is claimed by Liebermeister that sudden exposure to cold stimulates heat-production, Rosenthal disputes this {39} statement, and maintains that it is still to be regarded as doubtful whether the production of heat can be varied to suit the demands of sudden and temporary changes of temperature. With the admission of this doubt, the regulation of the temperature of the body, under the circumstances just referred to, is mainly accomplished through the influence of agencies favoring or checking the loss of heat. Since heat is largely brought to the surfaces of the body by the circulating blood, modifications in the fulness and rapidity of this superficial current produce corresponding differences in the amount of heat and moisture presented. Such variations are considered to be accomplished through the action of the vaso-motor nervous system, whose differing effects are apparent in the pale, cool skin and the flushed, warm surface.

The search for the regulation of such vaso-motor action has led to the view that the production of heat, as well as its dissipation, may be influenced from a nervous centre. Wood claims that the result of experiments made by him proves the existence of such a heat-centre in or above the pons. Although admitting the possibility of its being a muscular vaso-motor centre, he regards it rather as an inhibitory heat-centre, which acts, as suggested by Tscheschichin, by repressing the chemical changes in the constituents of the body through which heat is produced.

This view is objected to by Rosenthal, on the ground that the facts are not universally agreed upon, and their interpretation is somewhat vague. Even the increased production of heat as determined by Wood, if admitted, may be regarded as the result of a modified circulation.

The preservation of a normal range of temperature in general is to be recognized as the result of variations in the relation of heat-production to heat-dissipation. The causes which influence this relation may act from without or from within, and are regarded as producing their effect by means of the vaso-motor nervous system. The causes which act from within are those concerned in the febrile elevation of temperature. Whether the latter is associated with, or independent of, inflammatory processes, the question of first importance relates to the modification of physiological conditions. The causes of the physiological production of heat and its dissipation have already been referred to, and the same elements demand consideration in the pathological range of temperature so striking in fever.

Relatively accurate inductions with regard to the origin of febrile heat were first rendered possible by the experiments of Billroth and Weber. These observers found that the introduction of putrid material into the circulation of animals produced fever. It was afterward shown that various substances, not necessarily of a putrid character, might produce the same result.

From measurements with the calorimeter of the heat produced, it was concluded by Wood that in the fever of pyæmic dogs more heat was produced than in healthy, fasting dogs, although less than in high-fed, healthy dogs. An increased production of heat in the fevered animal is thus obvious, as his capacity to receive and assimilate food is considerably less than that of a high-fed, healthy dog. The calculations of Sanderson, referred to by Wood, based upon the analyses of eliminated carbonic {40} acid and urea, show that the febrile human subject produces very much more heat than the fasting, though less than the fully-fed, healthy, man.

An increased production of heat in fever is generally admitted, although it alone is not to be regarded as the essential feature in the elevated range of the temperature. The fasting man or animal under ordinary circumstances is not febrile, and an increased production of heat from full feeding in health, equal to that observed in fever, not being associated with fever, it is apparent that the retention of the produced heat is of importance for the existence of fever. Although it has been shown by various observers that more heat is dissipated during fever than in health, this increased loss is not in proportion to the increased production of heat. A persistent elevation of temperature is the necessary result. This elevation is subject to daily and hourly differences, as is the temperature of the healthy individual. These variations in the range of the febrile temperature are apparently due to an agency like that which dominates the course of normal temperatures--viz. a varying action of the vaso-motor nervous apparatus, as well as of that controlling the secretion of sweat, now permitting, now checking, the dissipation of the produced heat.

For the existence of the elevated temperature of fever, therefore, there is demanded the presence of an agent within the body which, as stated by Wood, shall act "upon the nervous system which regulates the production and dissipation of animal heat--a system composed of diverse parts so accustomed to act continually in unison in health that they become, as it were, one system and suffer in disease together." It may be that there exists, as claimed by Wood and Tscheschichin, a heat-centre independent of the vaso-motor and other centres, through which heat is dissipated, or it may be, as maintained by Rosenthal, that the vaso-motor system alone is concerned in the regulation of temperature. Such action may be inhibitory or excitant, according to the views of the one or the other author, without affecting the main question as above stated.

The elevation of temperature suffices to explain for the most part certain of the other phenomena of fever, as thirst, digestive disturbances, increased respiration, and emaciation. A coincident affection of various cerebro-spinal centres is demanded to explain the altered action of the heart and the numerous nervous symptoms which are to be found in fever. The agent producing such manifold effects is obviously no unit. It may be introduced from without or it may arise within the body, and its transfer to the nervous centres is undoubtedly accomplished through the circulation.

Among those agents which act from without are to be included the specific causes of infective diseases. It is probable that these produce the fever, as they occasion other symptoms of the disease, and their action may be regarded as direct, or indirect through the secondary products of their own vital changes. In the light of the existing facts the products of minute organisms developed outside the human body may give rise to fever when introduced, without the organism, into the body. The history of septicæmia contains numerous illustrations of the pyrogenetic properties of material produced in connection with wounded surfaces of the body exposed to the action of minute organisms. The introduction of blood of the same, or of a different animal, into the {41} circulation of a given animal is followed by fever, as is the injection of considerable quantities of water into the blood-vessels. The same is true of various chemical substances.

It is further obvious that the agents producing fever may arise within the body. The fever resulting from the deprivation of water, and from the destruction of tissues, are instances of the probable origin of pyrogenetic substances from the rapid metamorphosis of tissues.

It is suggested by Samuel that under given circumstances the fever may be sanatory. This view is based upon the probability that certain parasitic organisms are destroyed at such temperatures as may be produced within the body. The growth of the bacillus of malignant pustule takes place most vigorously at a temperature of 30.5° C. (95° F.), while its development is feeble at 40° C. (104° F.). The bacillus of tuberculosis, as shown by Koch, thrives at temperatures between 37° C. (98.6° F.) and 38° C. (100.4° F.), but its growth ceases at temperatures above 41° C. (105.8° F.). The spiral fibre of relapsing fever, which is present in the blood in great abundance at the beginning of the febrile onset, disappears at the close, the temperature being 42° C. (107.6° F.). It is not to be found in the intervals between the febrile paroxysms, but reappears a few hours before the recurrence of the fever. The history of intermittent fever suggests a similar relation between its cause and the febrile periods.

The value of pain as evidence of inflammation is merely relative. Its existence depends upon the presence of sensitive nerves, and those inflammations are the least painful which occur in parts where such nerves are fewest.

The pain of inflammation is attributable to the pressure upon the nerves of that product of the inflammation known as the exudation. This pressure becomes all the greater the more abundant the exudation, or the greater the obstruction offered to its diffusion throughout the inflamed part. The intense pain resulting from inflammation of the fascia or of the periosteum is thus explained, while an inflammation of the loose connective tissue may be diffused over a wide area with little or no pain. In the chronic varieties of inflammation, where the exudation is but scanty, and its accumulation extended over a long period of time, there may be no pain during the entire course of the inflammation.

Swelling remains for consideration as the most important of the four cardinal symptoms. Like the others, its presence is not absolutely essential. It may exist at one time in the course of the inflammation, and may be absent at another. Even a diminution in the size of an organ may suggest the existence of an inflammation, for the yellow and cirrhotic atrophies of the liver give evidence, respectively, of an acute and chronic inflammation of this organ.

The swelling of an inflamed part is due to the presence of an increased quantity of blood, and lymph, and to the exudation. These constituents of the swelling are not of equal importance. Although the quantity of blood in the part is increased, no considerable swelling is produced, provided the flow of blood and lymph from the part be unobstructed. The current of lymph through the larger lymphatics may be greatly increased, yet a decided swelling be absent, unless there is an obstruction to the passage of lymph from the inflamed region.

{42} The exudation is the most essential element of the swelling, and our knowledge of its origin and fate includes the most important features of the general pathology of the processes concerned.

The inflammatory exudation is represented by the accumulation, outside the blood-vessels, of material previously within them. The prevailing views concerning the manner of origin of this exudation, and its relation to inflammatory processes, are essentially due to the rediscovery by Cohnheim of the forgotten observation of Addison, that white blood-corpuscles pass through the apparently intact walls of the blood-vessels.

In the observation of the mesentery or other transparent part of a suitable animal, the changes taking place in inflammation are, at the outset, limited to the blood-vessels and their immediate vicinity. The vessels become dilated and the rapidity of the flow within them is soon diminished. In the veins particularly the white blood-corpuscles separate in considerable numbers from the general current and line the wall in constantly-increasing numbers, while the red corpuscles are borne along the middle of the stream. The white corpuscles stagnate, stick to the wall for a longer or shorter time, and often change their place, while the red corpuscles are in constant and progressive motion. In the capillaries a considerable number of white corpuscles are found in contact with the wall, but numbers of red corpuscles are associated with them. The formation of the exudation now begins by the passage of white corpuscles through the apparently intact wall of the veins and capillaries, especially of the former. Limited numbers, under ordinary circumstances, of red corpuscles also make their way through the walls of the capillaries. This is the phenomenon of emigration, and is associated with the amoeboid movements of the white corpuscles.

With the passage outward of the white and red corpuscles there is also the effusion of liquid material. Both the liquid and solid constituents continually escape and spread in all directions beyond the wall, following the course of the least resistance. It is probable that this course is defined by the pre-existing spaces within the tissues of the part, the lymph-spaces. The exudation is more abundant in parts richly provided with blood-vessels and in those containing the larger spaces; it is diminished where the vessels are less numerous or the surrounding parts more resistant, with smaller and fewer lymph-spaces. The resulting swelling is the less when ready opportunities for the diffusion and removal of the exudation by lymphatics and veins are presented, and when the material appears upon surfaces over which it may flow away.