SCIENCE FROM AN EASY CHAIR.
Press, Volume XLVIII, Issue 14376, 8 June 1912, Page 9
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SCIENCE FROM AN EASY CHAIR.
LYMPH IN BLOOD
(By Sib Rat Lan-kt.ster, X.C.8., F.R.S.)
(Special rights secured by "Tho Press.")
Most people do not kr.low even of tho existenco in their own bodies of a fluid called "the lymph," and of a system of vessels and spaces containing it which ramify liko tho b'.bod-vcsscls into every part of tho body. This arises from tho fact that the lymph is translucent and colourless. You can see the finest blood-vessels when the body tof a dead rat, cheep, or man is opened, because they aro filled with tho beautiful red blood, and appear ac a rich, coloured net-work. But the lymph and tho lymph-vessels escape notice, and, indeed, are invisible except the largest, because they are colourless. They remained unknown to anatomists long after arteries and veins, and the iino networks of hair-like vessels or capillaries connecting them, were thoroughly well studied. It is, when. one thinks of it',: a very notewortliv tending to cic>u> vihee us of the readiness with which we may (in tho absence of careful examination and attention) overlook tho n<>st weighty, things, that here is a groat system of vessels and. spaces in the human body and in that of other animals-, carrying on most important operations in our daily life, and yet nkst of us have never seen any. evidence of its existence, and never hold it in our mind's ovp as part of the great mechanism of tho animal body.
Tho lymph is. a clear, colourless fluid, with "corpuscles" —minuto nucleated cells or particles or protoplasm—floating in it. Tile liquid part is closely similar in its properties and chemical constitution to tiio liquid part of the blood. It, indeed, consists largely of the liquid part tA tho blood, which exudes from the iinest hair-like blood vessels or capillaries as they traverss the various tissues, and it is tho chief business of the ''lymphatics" or lymph-holding vessels to return this exuded liquid to the blood system which they do by joining—like tho rivulets of a river system —10 form two large trunks which open into the great bloodholding veins at the reg on where they approach the heart. The total amount of lymph in the lymphatic system is difficult to estimate, but it is larger in quantity than tho blood in the entire blocd-vascular system. A largo number of the delicate vessels of the lymphatic system take their origin just below the lining layer- of the intestine, and ramify through tho transparent membrane, which holds the coils of the intestines together, and is called the mesentery. The fatty or oily nuuerkus of toc-d pass through the lining "cells" of tho intestinal wall into these lacteal or milky lymphatics, and consequently in an animal killed and examned after a meal, the fluid in the lacteaLj lias a milky appearance, and renders tho "lymphatics" visible. They wero for this reason the first to be detected, and were known even in ancient times to anatomsts. The milky fluid in thorn was called "the chyle." Its milky appearance is due to the same cause as the white opaque appearance of milk, namely, to the presence of an immense number of immeasurably small particles of oil (fat) and a certain proportion of larger globules of the same nature. It was thus not difficult for tlie old anatomists to trace tho fine branches of tho lacteals unit'ng branch to,branch, and forming a large trunk—called the thoracic duct—about a quarter of an inch thick, which runs tip the inner face of the liackbono to tho neck, where it joins the great left subclavian vein, and pours its contents int. 3 the ble-od-etream which is there nearing the heart. A small trunk formed by the union of lympathic vessels from tho right side of the hend and neck and the right tipper limb opens into the right subclavian vein. Ij took some time to d scover this smaller trunk, since it is not brought to view by milky contents, and gradually it, was made out that there are innumerab'.e transDnrent branches opening into tho thoracic duct from the whole of the body, besides the milky-look'ng lacteals. branches which bring "limpid -, clear fluid, or-''lymph," from all tho viscera, from the*muscles, and from tho deeper Inyors of tho skin in every region of the body, right down to the toe*, fingers, and tongue tip. Tn fact, wherever the. Wood-vessels take b'.ood there are lymphatics bringing hack some of the liquid exudation of i the finest blood-vessels.
Whilst we distinguish in an animal body various "tissues" which have special properties and activities, and can lx> dissected out and delimited a* wo could disFoct and distinguish the. '■tissues" (flannel, silk, leather, whalebone, wadding, gold-thrcnd, etc.) making up an elaborate padded, stiffened brocaded, lined, and decorated costumo, we find that, unlike what is usual in a man-made costume, all tic ~irts of an animal body (the viscera, and tlieir lobes and suodivisions, the
blood-vessels, nerves, muscles, bones, etc.), arc covered and separated from one another, and at the same time, held together by a übiquitous, sort, spongy tissue, consisting of delicate threads and bands, enclosing spaces-some excessively minute and narrow, ethers larger —in which is a liquid. This is the great packing tissue of the body, .and is called ■ ''the connective tissue/ Its threads and bands have delicate, usually flat nucleated corpuscles (so-vailed "coils'") of transparent protoplasm, resting upon them and bathed by the liquid in the fine spaces. Tho thrtscb and bands are, indeed, the product of protoplasmic cells, builtor "u<])mi" by them, laid down by them as a snail leaves a slimy smear behind it as it crawls. It is not difficult to cut out transparent pieces of tlrs "connective tissue" from a recentlykilled animal, and to examine it with a very high rower of the microscope. You may then see the living protoplasmic corpuscles slowly "streaming ,, and {.hanging shape, and sometimes dividing (one into two), so as to form new corpuscles. I made my first acquaintance with theru when I was a student at Vienna with the great mie-o-scopist Strieker. We used tho glassclear connective tissue which forms the
'•cornea" of the eye cut from a freshly killed frog. In tlioso days tho part taken by these cells in inflammation was being discovered, the name "phagocyte" had not been invented, the part played by them and by bacteria in disease and the suppuration of wounds was unknown, and I had the privilege of introducing Lister's earliest researches on aseptic surgery and on the coagulation of the blood to tho notice of my friend and teacher.
This übiquitous "connective tissue" underlying the skin, pushing its way into and around every part of every structure in the body, is the "source" —tho reservoir, as it were—from which tho lymph stream and the finest lymphatic vessels take their origin. The question may very naturally bo asked, "How is it that the lymph* flows along tho channels provided by the transparent lymph vessels and is poured through 'tho thoracic duct' into tho gtvat vein near the heart" If we inject a suitable coloured fluid by means of a needle-pointed syringo into any ma.ss of connective tissue, wo can sco ■the fluid pass into the numerous lymph vessels previously invisible, and by a sort of photographic staining by silver nitrate v:o can make out tho lining pavement cells and the structure of the walls of th" lymphatics. Hut thcro is no muscular envelope, nothing like a. lymph-henrt in mammals, to drivo tho lymph along. There are valves or flexible flaps in the walls of tho lymph-vessels, as there aro in tho veins, and the lymph is driven to the heart by the intermittent pressure upon theso valved tubes, caused by tho movements of tho muscles and of the body. The valves, like those of the veins, prevent the flow of tho lymph backwards, but allow it to_ pass forward towards tho_ heart. This is shown by tho examination of a narcotised mammal (killed immediately after tho examination has been made). A glass tube is placed in tho thoracic duct, and about eight drops of lymph (which would havo been delivered into tho great vein) pass from it in a minute. If, however, tho animal's le<is are moved, as though in running, or if "massage" is applied to tho limbs —the pressure being directed from tho extremites towards tho heart —then a greatly increased flow of lymph is observed, as much as sixty drops in a minute! This is the chief explanation of tho value to our health of exercise, and also of tho importance of "massage" as a treatment in disease. They, entirely revolutionise the rate of flow of tho lymph, quickening it so greatly that tho physiological effect on tho general chemical processes going on in tho body cannot fail to bo most important. ,
Curiously enough,' whilst mammal? havo to depend entirely on pressure and , exercise for anything but tho slowest flow' of the lymph, the coldblooded vertebrates, fish, amphibia and reptiles (and even, some birds), have remarkable, rhythmically contracting, muscular sacs, which pump tho lymph from largo lymph-vessels into large veins, and " are called "lymphatic hearts." The eel and other fish havo them in the tail, but they are best seen in the common frog. There is an anterior pair, ono under each shoulder-blade, and another pair, ono on each hip. Each opens at one end into a largo "collecting' , lymphvessel, and at tho other end into a largo vein. They " beat " like a heart, but do not keep time with one another. Their muscular walls are formed by what is called "striated" muscular tissue (as are those of tho blood-heart), and they aro under tho control of branches of tho spinal no/yes. The movement of the hinder pair in a frog can bo seen through tho skin.
In man and all vertebrate animals the intestines, stomach and liver, heart and lungs (or swim-bladder) lie loose, except for a fibrous band of attachment in a. groat cavity (often divided into two or more chambers), which they (it fairly closely. The small space between thorn and the walls of the cavity is occupied by a liquid. This is lymph, and the- great cavity is a lymph-space. When this cavity is in its primitive form it is called the body cavity, or " ccclom. " In man and mammals it is divided into four chief chambers —tho peritoneal cavity (in which tho stomach, - intestine, find liver are- loosely attached and have a cerzaiu mobility), the right p'eura.l and left pleural cavity (one for each lung), and the pericardial cavity (for tho heart). These great chambers are par; of the lymiph-system, and co is tho lymph-hckl ng smiee around and within the brain and spinal cord, and so arc tho great spaces beneath the frogs .skin. If we look at tho structure of an earthworm or of one of the graceful marine -worms (Nereis or Arenicola), we gain a good deal of light as to the nature of the lymphatic system of vertebrates. Suppose you have killed a largo earthworm with chloroform! Then pin it out on a cork plate, and open it by a cut along the back with a fine pair of scissors. The point of your scissors passes through t-h*' muscular body-wall of mc worm into a great chamber filled with a clear liquid. Th r chamber is the '•cculom," and is the same structure as the pleural arid peritoneal chambers of the vertebrate. Hud it holds (proportionately) more, liquid. The liquid is "lymph,' , like that of the vertebrate, and has numerous protoplasmic colls floating in it There is comparatively little connective tissue in the earthworm. The> ccelom Is free and anhlockcd —the great viscera lie in it. There are some delicate, transparent bands of connective' tissue, but not much nor bulky. The wall of the ccslom itself is lined with connective tissue, and if it grew 4 greatly in bulk, and bound all the organs and muscles together, it would reduce the large cavity, tilling it up with rpongy tissue in the small interst'ees of which thero would be lymph. And so we should got a lymph system resembling that of vertebrates instead of one large chamber.
But what about the opening of the lymphatics into the blood-vessels? This ifi one of the interesting differences between the earthworm and the vertebrate. The earthworm and many marine worms have a beautiful system of vessels, containing a bright red blood, and forming true capillaries, connecting, arteries and veins. The heart is a long, rhythmically beating tube, extending along the whole length of the animal just above the intestine. There is no opening into it of the l-~ h-cavity. It is purely a respiratory blood-syrftem. pumping its fluid, coloured red by oxvgen-«M 2 j, KI . hscinoglobin into every part of the body, and
abundantly into tho fine capillaries of the skin, whero it seizes oxygen from tho outside and carries it to all the tissues, lne fact is that the ml respiratory element of tho blood which wo cail especially tho ha?ma cr ha-nial portion (the Greek word for red blocd is at/xa ) is here kept separate from tho nourishing aud elaborating element, _ tho lymph or lmyphat.c portion. So that we should, to be explicit. describe the blood of a- vertebrate as "hajuwlymph," a conjunction of Inema and lymph, which in tue more primitive eartliworm and seawonu have never eifected a junction! i n some closelyallied marine worms, however, a junction of these two is effected in another way. c know that in tho vertebrates the red blood corpuscles aro formed by detached bits of the same tissue, which becomes converted into capillaries, the iine-st blood-vesselo. X o w, in several marine bristle-footed worms (Giycera. Capitella, etc.) the tissue which should form the blood vascular system and ite red blood changes its modo of growth; it never lorms blood-vessels at all but divides into free red (hnemoglobinous) cells or red blood corpuscles, which float m the lymph of the coelom. There is no blood vascular system produced at all! Jhe h.-omal tissue breaks tin into red corpuscles, which, mixing with the lymph, bring it into the condition of ha-molymph, identical with the blood of vertebrates!
In tho molluscs, snails, whelks, oysters clams, and cuttle-fishes there is a further variation. The same two fluids and two systems of spaces are present as in the earthworm, but the 'coelomic space and fluid havo been nearly blocked up and obliterated by -the swelluig-up and great size of the proper hremal-ycsscls (only in rare cases is tho blood of mollusc red). There is stili left a pericardial coelom, a space around tho hearty and from this some, fine lymph-holding vessels ramify amongst the tissues, but the chief spaces in tho body aro dilated parts of the true hromal system. In insects and crustacea (say cockroach and lobster) this process is carried still further. Tho great coelom, so well developed in th* worms (annelids), and the sea-urchins and star-fishes, and retaining quite a largo development also in the vertebrates, is nowhere to be found. The swollen blood-vessels havo crushed it out of existence, except for certain sack-like remnants which enclose separately the ovaries, and the testes, and tho and havo each its opening to the exterior conveying tho products of those important organs to tho outer world. Thus we gain a brief insight into tho truo history of tho 'lymphatic system and its vicissitudes in the lower animals and in man.
