THEORY OF INFLAMMATION.

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very opposite of such as are most favourable for exertion, which are those of diminished capacity. Then again, the point is not yet finally settled, whether the capillary vessels possess of themselves a power of propelling their own blood, or it be forced through them by the action of the heart; or whether or not the two powers act in conjunction in circulating the blood, as seems the most probable at all events, these considerations present difficulties which, when added to the universal and potent influence of the nervous system, contribute greatly to the complexity of any investigation into the nature of inflammation. Of late years the subject has undergone renewed inquiry, and much assistance has been afforded by a closer and more accurate observation of parts actually under disease than appeared to have been given in times before; and the result has been, the pretty general admission of certain facts or data on which future theories may be more safely grounded.

THAT AN INCREASED QUANTITY OF BLOOD IS SENT TO AN INFLAMED PART, admits of demonstration: first, From the throbbing of the arterial trunks supplying it, which is an unequivocal sign of increased action; secondly, From the state of the part itself; viz., a. its unusual redness; b. the evident distention of its vessels; c. their actual dilatation or enlargement, as has been proved by experiment; d. the consequent admission of red blood into vessels which before were of insufficient calibre to admit any but the serous or finer and colourless parts of that fluid.

THAT THE BLOOD IN THE INFLAMED PART IS NOT ACCUMULATIVE, CONGESTIVE, OR STAGNANT, BUT IN CONTINUAL ACTIVE CIRCULATION THROUGH IT, is demonstrated-first, By the distended and enlarged state of the veins which convey it away; secondly, By the experimental fact, that more blood will flow within a given interval from those veins than from the correspondent vessels on the opposite or healthy side of the body-a result Mr. Lawrence has uniformly obtained in letting blood at the same time from fellow venous trunks in the arms of a man, one of which only was in a state of inflammation; thirdly, From the circumstances of inflamed parts, when cut into, exhibiting

blood of the arterial character, and yielding it more rapidly and in greater profusion than correspondent or contiguous parts that are in health.

CONDITION OF THE CAPILLARIES. -This brings us to the pith and marrow of the question. And from what has gone before it appears, that the blood, which is sent to the inflamed part in augmented proportion, so far from being congested or anywise stagnant, or even meeting with any impediment in its course, is actually flowing with increased velocity, as well as fulness of current, through the capillaries, as is made manifest both by its character and by the plethora of the vessels that conduct it away. Were it detained in the capillaries, or retarded in its course through them, it would undergo the changes naturally consequent on its protracted absence from the heart, and turn purple or black in its hue; and, moreover, would issue but tardily from the venous trunks: whereas, we know that the contrary of both these suppositions is the case. In fine, it would appear, from what facts and evidence we are able to collect, we must come to the conclusion, forced and even unnatural as it may at first seem to us, that the blood is actually circulating through the capillary system of a part under inflammation both in greater proportion and with more rapidity than through the same vessels in a state of health: the only rationale of which extraordinary or preternatural performance I can offer is, that the vascular powers are roused to it and rendered eapable of it, through augmented energy inspired into them by the nervous system. Let us see how these explanations tally with the symptoms.

RATIONALE OF THE REDNESS.-This symptom is evidently owing to augmentation of blood in the inflamed part; filling all its vessels to repletion, and distending numerous ones with red blood whose calibre in health is too small to admit but the finer and colourless particles of that fluid. The character or shade of the redness is owing to the quality of the blood, and also, in some measure, to the natural vascularity of the affected part: the florid scarlet complexion of the part being attributable to the arterial character of the current of blood; while tendons and ligaments assume less redness under inflammation than skin and muscle,

RATIONALE OF THE HEAT,

61 from the circumstance of their being naturally less vascular. I say "naturally" so; for, as Mr. Hunter tells us, "parts inflamed appear to become more vascular;" though he imagines that appearance may be owing to the dilatation of the capillary vessels. The same distinguished pathologist placed the ear of a rabbit in a situation where it froze; after which he thawed it: this occasioned intense inflammation. In this condition the animal was killed, and the two ears injected and afterwards dried. The uninjured ear dried clear and transparent, beautifully displaying its arborescent vessels from a single trunk; but the inflamed ear dried thick and perfectly opaque, at the same time exhibiting vessels double in number, and of larger size; and instead of one, two principal trunks.

RATIONALE OF THE HEAT.-An animal body derives its heat from its circulating blood. That fluid in its passage through the lungs undergoes, by exposure to the air, certain changes, in consequence of which it acquires heat in a latent form, to be evolved in a sensible one in the course of its circulation over the body: consequently, any part through which a larger quantity of blood circulates than natural will be hotter than natural. At least, as was before observed, this will be the case with parts whose temperature is by nature below the standard of heat of the body, which is from 98° to 100° Far. Not but that more heat is actually evolved in every situation under inflammation; but, as was before stated, it does not appear to be accumulative, or but to a trifling degree so: it seems to pass off almost as quickly as produced, operating on the sensations of the patient without, in any thing like a proportionate degree, raising the actual temperature of his body. Mr. Hunter conceived that the body had the power of generating cold as well as heat: and though his proofs of this are, perhaps, rather of a negative than positive kind, we may certainly go so far as to say, that it exerts, at all times and under all circumstances when required, operations to abate or carry off excessive heat. Our theories on the subject of animal heat are not yet sufficiently matured to enable us to speak very plainly or decidedly on the present point. The nervous system is probably very influential; and this will neces

sarily add to the complexity of any rationale of heat one might have to offer.

THE RATIONALE OF THE PAIN is referrible, exclusively, to the nervous system. The nerves of the part under inflammation appear to be in that state of excitement, that causes which under ordinary circumstances would create but common sensation, now produce pain. One cause appears evident in the tumefied condition of the part itself: the general bloated and tense state of the inflamed tissues must operate in pinching the nervous filaments entering into their composition, at the same time stretching many of them considerably beyond their natural tone. In parts of an unyielding nature, such as tendons and ligaments, the pain is often violent, at the same time peculiar in its kind, owing to the severity of the compression the nerves must experience during the more tensely swollen condition of the parts. Any thing that tends to relieve distention to a certain degree, at the same time relieves the pain felt in the part: during a violent and dangerous inflammation in my own hand, I experienced considerable mitigation of the pain whenever I maintained it in a position with the hand elevated, and the arm, as much as possible, extended; the return of blood through the veins being thereby greatly facilitated. On this principle it is that pain is felt augmented at every throb or fresh distention the inflamed part undergoes. Gradations in pain and kinds of pain, which in course are both very variable, will in a degree admit of explanation on the score of the number and distribution of the nerves the part inflamed may contain; the yielding or unyielding texture of the part; the violence of the inflammation; and also, in some measure, on the nature of the exciting cause: after all, however, we shall find ourselves forced to confess, that the morbid sensibilities of the nerves will not admit of complete elucidation until we have become better acquainted with their operations in health.

RATIONALE OF THE SWELLING.-The tumour of an inflamed part is ascribable to two causes :-to the immoderate distention of its vessels with blood, and to effusion from their exhalent terminations of part of that blood in the form of serous

CAUSES OF INFLAMMATION.

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fluid and coagulable lymph into the cellular interstices of the inflamed and surrounding textures. In the early stages, the swelling seems attributable simply to distention: effusion, however, speedily supervenes, and in the latter stages constitutes the major part of the tumour, imparting a degree of plumpness and firmness to it, and often remaining, even after the inflammatory action has subsided. The firm solid feel the tumour has about its middle or more prominent part, when the inflammation runs highest, is owing to the effusion of a mass of gelatinous matter, which, on examination, turns out to be the same as the coagulable lymph or fibrine of the blood; while into the surrounding parts, where the swelling is less prominent, and has a softer and more doughy feel, serous effusion is found mingled with the solid deposition. In anasarcous or oedematous affections, the effusion seems altogether of a fluid or serous nature.

CAUSES OF INFLAMMATION.

INFLAMMATION may arise in a great variety of ways, some of which are obvious to us, while others are either mysterious in their nature, or else altogether concealed from our view. Numerous and various however as these are, they admit of classification, conveniently enough, into accidental, spontaneous, and sympathetic. An inflammation is said to be accidental when its exciting cause is self-evident, and in itself is commonly extrinsic to the body; comprehending all such as arise from mechanical and chemical injuries and irritations of all kinds, as well as such as are ascribable to atmospheric vicissitudes and excitations. Spontaneous inflammations are those that are imagined to spring up of their own accord; though, perhaps, it is better to say, without any apparent or assignable cause: they are mostly what are called inward affections. Sympathetic inflammations owe their production to disease in other parts of the body.

MECHANICAL INJURIES comprise wounds and contusions and abrasions of all sorts; sprains, dislocations, and fractures; undue exertion of any part or organ, or of the body altogether, what, in hunter's phrase, is called being "over-marked.".