INHUMATION

INHUMATION, in chemistry, a method of digesting substances, by burying the vessel in which they are contained in horse-dung or earth.

Injection. INJECTION, the forcibly throwing certain liquid medicines into the body by means of a syringe, tube, clyster-pipe, or the like.

Anatomical Injection, the filling the vessels of a human, or other animal body, with some coloured substance, in order to make their figures and ramifications visible. The best account of the method of injecting the vessels of animals, is that by the late Dr. Monro, published in the Medical Essays, vol. i. p. 79.

"The instrument with which the liquor is commonly thrown into the vessels is a tight easy going syringe of brass, to which several short pipes are fitted, and can be fixed by screws, the other extremities of these pipes being of different diameters without any screw, that they may slide into other pipes, which are so exactly adapted to them at one end, that when they are pressed a little together, nothing can pass between them: and because their cohesion is not so great as to resist the pushing force of the injection, which would drive off this second pipe, and spoil the whole operation; therefore the extremity of this second sort of pipes, which receives the first kind, is formed on the outside into a square, bounded behind and before by a rising circle, which hinders the key that closely grasps the square part from sliding backwards or forwards; or a bar of brass must stand out from each side of it to be held with the fingers. The other extremity of each of these second sort of pipes is of different diameter; and near it a circular notch, capable of allowing a thread to be sunk into it, is formed; by this, the thread tying the vessel at which the injection is to be made, will not be allowed to slide off.

"Besides this form described, common to all this second sort of pipes, we ought to have some of the larger ones, with an additional mechanism, for particular purposes; as, for instance, when the larger vessels are injected, the pipe fastened into the vessel ought either to have a valve or a stop-cock, that may be turned at pleasure, to hinder any thing to get out from the vessel by the pipe; otherwise, as the injection, in such a case, takes time to coagulate, the people employed in making the injection must either continue all that while in the same posture; or, if the syringe is too soon taken off, the injected liquor runs out, and the larger vessels are emptied. When the syringe is not large enough to hold at once all the liquor necessary to fill the vessels, there is a necessity of filling it again. If, in order to do this, the syringe was to be taken off from the pipe fixed in the vessel, some of the injection would be lost, and what was exposed to the air would cool and harden; therefore some of the pipes ought to have a reflected curve tube coming out of their side, with a valve so disposed, that no liquor can come from the straight pipe into the crooked one, but, on the contrary, may be allowed to pass from the crooked to the straight one: the injector then, taking care to keep the extremity of the reflected pipe immersed in the liquor to be injected, may, as soon as he has pushed out the first syringeful, fill it again by only drawing back the sucker; and, repeating this quickly, will be able to throw several syringefuls into the vessels.

"All these different sorts of pipes are commonly made of brass. Injection.

"The liquors thrown into the vessels with a design to fill the small capillary tubes, are either such as will incorporate with water, or such as are oily; both kinds have their advantages and inconveniences, which I shall mention in treating of each, and shall conclude with that which I have found by experience to succeed best.

"All the different kinds of glue, or ichthyocola, syths, common glue, &c. dissolved and pretty much diluted, mix easily with the animal-fluids, which is of great advantage, and will pass into very small vessels of a well-chosen and prepared subject, and often answer the intention sufficiently, where the design is only to prepare some very fine membrane, on which no vessels can be expected to be seen so large as the eye can discover whether the transverse sections of the vessels would be circular, or if their sides are collapsed. But when the larger vessels are also to be prepared, there is a manifest disadvantage to the usefulness and beauty of the preparation; for if nothing but the glutinous liquor is injected, one cannot keep a subject so long as the glue takes of becoming firm; and therefore, in dissecting the injected part, several vessels will probably be cut and emptied. To prevent this, one may indeed either soak the part well in alcohol, which coagulates the glue; but then it becomes so brittle, that the least handling makes it crack; and if the preparation is to be kept, the larger vessels appear quite shrivelled, when the watery part of the injection is evaporated: or the efflux of the injection may be prevented, by carefully tying every vessel before we are obliged to cut it; still, however, that does not hinder the vessels to contract when the glue is drying. If, to obviate these difficulties, the glutinous liquor should first be injected in such quantity as the capillary vessels will contain, and the common oily or waxy injection is pushed in afterwards to keep the larger vessels distended, the wax is very apt to harden before it has run far enough; the two sorts of liquors never mix to mix irregularly, and the whole appears interrupted and broken by their soon separating from each other; which is still more remarkable afterwards, when the watery particles are evaporated.

"Spirits of wine coloured mixes with water and oils, and so far is proper to fill the very smaller vessels with; but, on the other hand, it coagulates any of our liquors it meets, which sometimes block up the vessels so much, that no more injection will pass; then it scarce will suspend some of the powders that prove the most durable colours; and as it entirely evaporates, the vessels must become very small; and the small quantity of powder left, having nothing to serve for connecting its particles together, generally is seen so interrupted, that the small ramifications of vessels rather have the appearances of random scratches of a pencil, than of regular continued canals.

"Melted tallow, with a little mixture of oil of turpentine, may sometimes be made to fill very small vessels, and keeps the larger ones at a full stretch; but where any quantity of the animal liquors are still in the vessels, it is liable to stop too soon, and never can be introduced into numbers of vessels which other liquors enter; and it is so brittle, that very little handling.

Injection. ling makes it crack, and thereby renders the preparation very ugly (A).

"The method I have always succeeded best with, in making what may be called subtile or fine injections, is, first to throw in coloured oil of turpentine, in such a quantity as might fill the very small vessels; and, immediately after, to push the common coarse injection into the larger ones. The oil is subtile enough to enter rather smaller capillary tubes than any colouring can; its resinous parts, which remain after the spiritous are evaporated, give a sufficient adhesion to the particles of the substance with which it is coloured, to keep them from separating, and it intimately incorporates with the coarser injection; by which, if the injection is rightly managed, it is impossible for the sharpest eye to discover that two sorts have been made use of (B).

"All the liquors with which the vessels of animals are artificially filled, having very faint, and near the same colours, would not at all appear in the very small vessels, because of their becoming entirely diaphanous, without a mixture of some substance to impart its colour to them; and where several sorts of even the larger vessels of any part were filled, one sort could not be distinguished from another, unless the colour of each was different; which has likewise a good effect in making preparations more beautiful. Wherefore anatomists have made use of a variety of such substances, according to their different fancies or intentions; such as gamboge, saffron, ink, burnt ivory, &c. which can be easily procured from painters. My design being only to consider those that are fit to be mixed with the injecting liquors proposed to fill capillary vessels, which is scarce ever to be done in any other, except the branches of the arteries and of some veins, I shall confine myself to the common colours employed to these last named two sorts of vessels, which colours are red, green, and sometimes blue, without mentioning the others which require very little choice.

"Anatomists have, I imagine, proposed to imitate the natural colours of the arteries and veins in a living creature, by filling the arteries with a red substance, and the veins with a blue or green: from which, however, there are other advantages, such as the strong reflection which such bodies make of the rays of light, and the unaptness most such bodies have to transmit these same rays, without at least a considerable reflection of the rays peculiar to themselves; or, in other words, their unsuitness to become completely pellucid; without which, the very fine vessels, after being injected, would still be imperceptible. The animal or vegetable substances made use of for colouring injections, such as cochineal, laque, rad. anebuse, brazil-wood, indigo, &c. have all one general fault of being liable to run into little knots which stop some of the vessels; their colour fades sooner when kept dry; they more easily yield their tincture when the parts are preserved in a liquor; and rats, mice, and insects, will take

them for food: for which reasons, though I have frequently succeeded in injecting them, I rather prefer the mineral kind, such as minium or vermilion for red; of which this last is, in my opinion, the best, because it gives the brightest colour, and is commonly to be bought finely levigated. The green-coloured powder generally used is verdigrease; but I rather chuse that preparation of it called distilled verdigrease; because its colour is brighter, and it does not so often run into small knots as the common verdigrease, but dissolves in the oily liquors.

"The method of preparing the injection composed of these materials, is to take, for the fine one, a pound of clear oil of turpentine, which is gradually poured on three ounces of vermilion, or distilled verdigrease finely powdered, or rather well levigated by grinding on marble; stir them well with a small wooden spatula till they are exactly mixed, then strain all through a fine linen rag. The separation of the grosser particles is, however, rather better made, by pouring some ounces of the oil upon the powder, and, after stirring them together strongly, stop rubbing with the spatula for a second or so, and pour off into a clean vessel the oil with the vermilion or verdigrease suspended in it; and continue this sort of operation till you observe no more of the powder come off; and all that remains is granulated. The coarser injection is thus prepared: Take tallow, 1 pound; wax, bleached white, 5 ounces; salad oil, 3 ounces; melt them in a skillet put over a lamp; then add Venice turpentine, 2 ounces; and as soon as this is dissolved, gradually sprinkle in of vermilion or verdigrease prepared, 3 ounces; then pass all through a clean, dry, warmed linen-cloth, to separate all the grosser particles; and, when you design to make it run far into the vessels, some oil of turpentine may be added immediately before it is used.

"The next thing to be considered, and indeed what chiefly contributes to the success of injections, is the choice and preparation of the subject whose vessels are to be filled.

"In choosing a fit subject, take these few general rules: 1. The younger the creature to be injected is, the injection will, ceteris paribus, go farthest, and vice versa. 2. The more the creature's fluids have been dissolved and exhausted in life, the success of the operation will be greater. 3. The less solid the part designed to be injected is, the more vessels will be filled. 4. The more membranous and transparent parts are, the injection shows better; whereas, in the solid very hard parts of a rigid old creature, that has died with its vessels full of thick strong blood, it is scarce possible to inject great numbers of small vessels.

"Therefore, in preparing a subject for injecting, the principal things to be aimed at are, To dissolve the fluids, empty the vessels of them, relax the solids, and prevent the injection's coagulating too soon. To an-

Injection. answer all these intentions, authors have proposed to inject tepid or warm water by the arteries, till it returns clear and untinged by the veins, and the vessels are thereby so emptied of blood, that all the parts appear white; after which, they push out the water by forcing in air; and, lastly, by pressing with their hands, they squeeze the air also out. After this preparation, one can indeed inject very subtilly; but generally there are inconveniences attend it. For in all the parts where there is a remarkable tunica cellulosa, it never misses to be full of the water, which is apt to spoil any parts designed to be preserved either wet or dry; and some particles of the water seldom miss to be mixed in the larger as well as smaller vessels with the oily injection, and make it appear discontinued and broken: wherefore it is much better to let this injection of water alone, if it can be possibly avoided, and rather to macerate the body or part to be injected a considerable time in water, made so warm (c) as one can hold his hand easily in it; taking care to keep it of an equal warmth all the time, by taking out some of the water as it cools, and pouring in hot water in its place; by which the vessels will be sufficiently softened and relaxed, the blood will be melted down, and the injection can be in no danger of hardening too soon; whereas, if the water is too hot, the vessels shrink, and the blood coagulates. From time to time we squeeze out the liquids as much as possible at the cut vessel by which the injection is to be thrown in (d). The time this maceration is to be continued, is always in proportion to the age of the subject, the bulk and thickness of what we design to inject, and the quantity of blood we observe in the vessels, which can only be learned by experience; at least, however, care ought to be taken, that the whole subject, or part macerated, is perfectly well warmed all through; and that we continue the presure with our hands, till no more blood can be brought away, whatever position we put the subject in.

When the syringe, injections, and subject, are all in readiness, one of the second sort of pipes is chosen, as near to the diameter of the vessel by which the injection is to be thrown as possible; for if the pipe is too large, it is almost needless to tell it cannot be introduced. If the pipe is much smaller than the vessel, it is scarce possible to tie them so firmly together, but, by the wrinkling of the coats of the vessel, some small passage will be left, by which part of the injection will spring back on the injector, in the time of the operation, and the nearest vessels remain afterwards undistended, by the loss of the quantity that oozes out. Having chosen a fit pipe, it is introduced at the cut orifice of the vessel, or at an incision made in the side of it; and then a waxed thread being brought round the vessel, as near to its coats as possible, by the help of a needle, or a flexible eyed probe, the surgeon's knot is made with the thread, and it is drawn as firmly as the thread can allow; taking care that it

shall be sunk into the circular notch of the pipe all round, otherwise it will very easily slide off, and the pipe will be brought out probably in the time of the operation, which ruins it.

"If there have been large vessels cut, which communicate with the vessels you design to inject, or if there are any others proceeding from the same trunk, which you do not resolve to fill, let them be all carefully now tied up, to save the injected liquor, and make the operation succeed better in the view you then have."

"When all this is done, both sorts of injections are to be warmed over a lamp, taking care to stir them constantly, lest the colouring powder fall to the bottom and burn (e). The oil of turpentine needs be made no warmer than will allow the finger to remain in it, if the subject has been previously well warmed in water; when the maceration has not been made, the oil ought to be scalding hot, that it may warm all the parts which are designed to be injected. The coarse injection ought to be brought near to a boiling. In the mean time, having wrapt several folds of linen round the parts of the syringe which the operator is to grip, and secured the linen with thread, the syringe is to be made very hot by sucking boiling water several times up (f), and the pipe within the vessel is to be warmed by applying a sponge dipped in boiling water to it (g).

"After all is ready, the syringe being cleared of the water, the injector fills it with the finer injection; and then introducing the pipe of the syringe into that in the vessel, he presses them together, and either with one hand holds this last pipe firm, with the other grips the syringe, and with his breast pushes the sucker; or, giving the pipe in the vessel to be held by an assistant, in any of the ways mentioned in the description of these sorts of pipes, he grips the syringe with one hand, and pushes the sucker with the other, and consequently throws in the injection, which ought to be done slowly, and with no great force, but proportioned to the length and bulk of the part to be injected and strength of the vessels. The quantity of this fine injection to be thrown in is much to be learned by use. The only rule I could ever fix to myself in this matter, was to continue pushing till I was sensible of a stop which would require a considerable force to overcome. But this will not hold where all the branches of any vessel are not injected; as for instance, when the vessels of the thorax only are to be injected: for the aorta bears too great a proportion to the branches sent from it, and therefore less fine injection is requisite here. As soon as that stop is felt, the sucker of the syringe is to be drawn back, that the nearest large vessels may be emptied. Then the syringe is taken off, emptied of the fine injection, and filled with the coarser, which is to be pushed into the vessels quickly and forcibly, having always regard to the strength and firmness of the vessels, bulk, &c. of the part. Continue to thrust the sucker, till a full stop, or a sort of push backwards,

wards is felt, when you must beware of thrusting any more, otherwise some of the vessels will be bursted, and the whole, or a considerable share of the preparation you designed, will be spoiled by the extravasation; but rather immediately stop the pipe by the turn-cock, and take out the syringe to clean it, and allow sufficient time for the coarse injection to coagulate fully, before any part is dissected. Ruysch, immediately after throwing in the injection, put the body into cold water, and stirred it continually for some time, to prevent the vermilion to separate from the tallow.