NOT SIMPLY A CHEMICAL QUESTION. 23 secondly, by washing away from it, in a dissolved state, whatever elements of its tissue have become worn out and useless. Thus, e. g., with the brain: the carotid artery carries blood to that organ; the jugular vein carries it back; and therefore, theoretically speaking, there must be this difference between the contents of the two vessels-that the blood of the jugular vein will be destitute, comparatively, of the materials necessary for renovation of the brain, (the phosphorus, the fat, &c.,) and will contain, instead of them, the effete products or waste of the brain, formed in the progress of its function,-chiefly perhaps consisting of carbonic acid, the phosphates, water, and other oxidized elements of its constitution; and then, as a final result of this process, the blood which has traversed the brain, and undergone the change in question, presently goes to other organs-organs of excretion, such as the lungs or kidneys, Analysis of the Composition of Healthy Venous Blood. * 24 ELEMENTS OF BLOOD DISTINGUISHED. where the phosphates and carbonic acid get eliminated from the system. If this were the whole history of the blood, its investigation in disease would be comparatively easy. But a chief difficulty in the study is this; that the blood undergoes changes of its own-undergoes what I can hardly call anything else than a process of growth. In addition to receiving new matter from the food, and old matter from the tissues, -in addition to feeding the several organs, and supplying the several excretions of the body, it does also itself undergo, as I have said, progressive changes of its own, analogous to the growth of the solid tissues. For the new materials which are derived to it from the food are not blood at the time of their addition; they are crude, immature products, which subsequently ripen within the stream of the circulation, under the influence of the maturer blood, and conformably to its composition. To some of you, perhaps, the view here suggested, of the blood undergoing development akin to growth, may be new and strange. There is an early prejudice, which makes us consider solidity of structure an indispensable preliminary for the residence and manifestation of life. Still, in spite of that prejudice, and in spite of the fluidity of the blood, you may safely believe that that red fluid is a living, growing mass; that the process of blood-formation is not the mere infusion of certain ready-made materials from without, but is as truly a process of growth as the development of cartilage or muscle. If the power of resisting change-if the power of converting things to its own type, and perpetuating its own constitutionbe signs of life in an element or portion of the body, I know none which possesses these qualities in a higher, if in so high, a degree as the blood. And further, in recalling its anatomy, you will be confirmed in this view. You will remember that, in all other elements of the body, the abundance of cell-development which you meet with, measures the activity and constancy of growth; and if you put a drop of blood under the microscope, and compare it with a patch of equal size of liver, or of brain, you are at once enabled to judge how immeasurably greater is the developmental activity in the blood; or if you look at a drop of fluid from the thoracic duct, you observe myriads of cell-germs there-germs which it is the chief, and perhaps the only, object of the lacteal and lymphatic systems to provide, and which attain their maturity, and fulfil their purpose, only when received into the blood. And not only does the blood live and grow; but, in the mature animal, its life and growth must precede all other life and growth in the body; for first it grows, next other organs grow at its expense. What I have said will suggest to you, how many liabilities to disease are included in the circumstances to which the blood is exposed; how easily morbid ingesta may become commingled with it as causes of change; how easily matters may be retained in it, which various distant organs ought to eliminate; how easily its own progressive development may be interfered with, arrested, or deranged. SIMILAR CLASSIFICATION OF MORBID PHENOMENA. 25 The enumeration, too, that I have given of its functions in health, will show you sufficiently what particular difficulties belong to any investigation of its changes in disease. In the first place, the extreme rapidity with which all its changes occur, the consequent transientness of the phenomena, and the minute quantities in which several of the ingredients exist, oppose great obstacles to the research; but still greater embarrassment is caused by the extreme complication of the fluid. By "complication," I do not mean merely that it contains a large number of ingredients; but that those ingredients correspond to different dates of time, to different degrees of development, to different organs of formation. Mentally we can see with perfect distinctness, that in every porringer of blood drawn by the phlebotomist there do in reality co-exist three forms of blood-viz., 1st, blood not yet ripe, but in course of development-perhaps I should rather call it matter in a transition-state from food to blood; 2dly, blood which is already perfect, and which, at the moment of its abstraction, was actually doing the work of the economy; 3dly, blood which had done its work and was worn out; or, to speak more exactly, the waste material of those various organs and tissues which the blood had previously nourished. Mentally, I say, we can separate these three kinds of blood, but experimentally we cannot. They are mixed together-past, present, and future, (the blood of yesterday, the blood of to-day, and the blood of to-morrow,) and we have no method of separating them. In all probability, the fibrin and extractive matters represent the waste products of the active elements of the body, and exist in the blood as effete material in the way to be eliminated; representing what just now, by a figure of speech, I called the blood of yesterday. Of the fibrin, I shall have plenty to say presently, and shall then explain to you why I consider it as an effete product in the blood. Of the extractive matters I know too little for me to dare to say much; hardly an endeavour has yet been made by any competent physiological chemist to refer them to the several organs in which they probably originate. Dr. Franz Simon, who has done with them more than any other chemist, divides them according to their respective menstrua into water-extract, alcohol-extract, proof-spirit-extract; but (as I need hardly suggest to you) that is not the sort of division likely to be useful to us in our present subject: the only physiological division would be one referring them severally to the organs whose effete products they represent: showing such an one to be brain-extract, another muscle-extract, &c. &c. It is desirable, gentlemen, so far as may be possible in treating of blood-diseases, to contemplate them in the manner suggested in the physiological retrospect I have made, and to take them in some such order as the following: First, diseases depending on morbid ingestion; secondly, diseases depending on increase, arrest, or alteration of the excretions; thirdly, diseases depending on modification of the blood's own growth and development. I. Morbid Ingestion. This is, in fact, known to you under the other name of poisoning. But when we have a patient suddenly 26 DISEASED CONDITION FROM MORBID INGESTION. dying or presenting symptoms under the effects of an active drug, we are sometimes apt to forget how important a part the blood plays in the production of phenomena. The symptoms of blood-disease are, in fact, generally quite lost in those of some secondary local affection. Where alcohol has been taken, the remarkable cerebral phenomena induce one to say that "it has got into the patient's head;"-and so it has; but its presence there has been preceded by its solution in the blood; and if a quantity of blood should be withdrawn at the time when alcoholic excitement is at its height, the process of distillation would conclusively attest the presence of the agent in question. You are, I dare say, aware of Magendie's celebrated experiments with poisons, particularly of those which he undertook to illustrate the transference of poisons by the blood. There are certain strong poisons, such as the wourali, which very rapidly diffuse their action over the entire system if a small portion be inserted into a recent wound. A little wourali thus inserted into an incision in a dog's foot would very rapidly prove fatal, under all ordinary circumstances; but Magendie found that if he previously tied the femoral vein, so as to prevent the general system of the circulation being contaminated by the poison, the symptoms were almost indefinitely postponed; he found, however, that directly he loosened his ligature on the vein, the poison (having passed on into the circulation) began to operate, and soon produced its characteristic fatal results. He invented, too, an ingenious way of demonstrating this still more strikingly; he would amputate a dog's leg, all but the artery and vein, so that the vessels should be the only medium of connection; or, more than this, he would divide these vessels, and join their upper to their lower sections by bits of quill or of catheter, still letting the blood flow on through the severed limb by means of these artificial pipes; and, not the less, did the symptoms of poison arise when there was no continuity of living tissue, no communication whatever except the flowing contaminated blood. The same is true in respect of cases of slower operation: in a peasant, who has been eating diseased rye-bread for some weeks, and who presently, in consequence, has dry-gangrene of the extremities; or in a painter, who for months or years has been exposed to the poisonous contact of lead, and who has got paralysis of the extensor muscles of the wrist, with perhaps other nervous injury beside; or in a gilder, who has been for a similarly long period, inhaling the vapours of mercury, and is palsied in consequence;-in any such case, say, you must not forget that the disease of the blood is the first link in the chain of cause and effect, and that the local affection, the excitement of brain, or the paralysis of muscles, or the obliteration of blood-vessels in the cases I have cited, or indeed any other morbid affection of a tissue or organ under similar circumstances, depends on that tissue or organ being nourished by a previously contaminated blood. If you take into the stomach a little rhubarb or iodide of potassium, and find traces of the drug in a few minutes in the urine, you know that, before arriving at the kidney, this material must have traversed the circulation; that it must have been absorbed I from the intestinal canal, have been dissolved in the serum, and literally have formed part of the blood during the time that elapsed between its absorption and its discharge. You see that this is pretty nearly the same thing as occurs in the natural processes of organic conversion. The urea, which the kidney naturally secretes, has not been developed in that organ, but has been formed at a distance from it has been formed, in all probability, as a part of the series of chemical changes which occur in the active tissues of the body during the performance of their functions; then, in order to reach the kidney, has formed part of the stream of circulating blood, dissolved in its serum, and detectable there by chemical procedure. While on this subject, too, I may take the opportunity of mentioning, though I shall again have occasion to recur to it,-that the organs which display these secondary affections under the influence of poisons in the blood will always have appropriated a certain proportion of the poison into their substance, and will generally display it under chemical treatment, even more strikingly than the blood itself. Thus, for instance, in the post-mortem examination of a paralytic looking-glass silverer, you may have the certainty of discovering traces of mercury in the substance of the nervous centres, &c. Now, to the affection of the blood by morbid ingesta, there are limitations set by nature which it may be well to consider. 1. A variety of poisons which would prove instantaneously fatal if they could enter the blood, are precluded from entering it at all events rapidly. The mineral acids, for instance, would at once coagulate the albumen and destroy the fluidity of the blood; but this act is impossible in reality; for their first chemical action being exerted on the tissue with which they come into primary contact, they begin by disorganizing this, coagulating all the albumen in its capillaries, arresting its circulation, and thus opposing an effectual barrier to their own direct action on the blood of the general circulation. I think it little less than certain, though I have not the means of demonstrating it to you, that the action of corrosive sublimate is very importantly limited and retarded by this process; and I may suggest it, as a very proper subject for inquiry, whether the pneumonia which so often follows the action of corrosive poisons, may not, in some instances, depend on a mechanical stasis, or interference with the capillary circulation in the lungs, by means of coagulated albumen, which has been conveyed in the blood from the seat of the primary lesion, and has become arrested in the next ensuing minute vessels to which the circulation had hurried them. There is another limit to the possibility of the blood's being poisoned, and this one acts almost or quite universally. I allude to the extreme rapidity of excretion, and I may inform you that this faculty, which forms an all-important provision for the safety and integrity of the blood, constitutes likewise (as you may conceive) a main source of difficulty in all chemical endeavours to demonstrate the passage of drugs and poisons through the circulation. I have already stated to you (and you may easily illustrate it for yourselves), that the elimination of a matter by one organ or surface of the body |