Part 17

A jar, six inches long and half an inch wide, graduated to,05 cubic inches, having a tight stopper adapted to it, was filled with nitrogene, which is a gas incapable of combining with, and possessing no power of a action upon venous blood. A large orifice was made in the vein of a tolerably healthy man, and the stopper removed from the jar, which was brought in contact with the arm so as to receive the blood, and pressed close against the skin, in such a way as to leave an orifice just sufficient for the escape of the nitrogene, as the blood flowed in. When the jar was full, it was closed, and carried to the pneumatic apparatus, the mercury of which had been previously a little warmed. A small quantity of the blood was transferred into another jar to make room for the gas. The remaining quantity equalled exactly two cubic inches; to this was introduced as speedily as possible, eleven measures equal to,55 cubic inches of nitrous oxide, which left a residuum of ¹/₃₂ only, when absorbed by boiled water, and was consequently, perfectly pure. On agitation, a rapid diminution of the gas took place.

In the mass of blood which was opaque, but little change of color could be perceived; but that portion of it diffused over the sides of the jar, was evidently of a brighter purple than the venous blood.

It was agitated for two or three minutes, and then suffered to rest; in eight minutes it had wholly coagulated; a small quantity of serum had separated, and was diffused over the coagulum. This coagulum was dark; but evidently of a more purple tinge than that of venous blood; no gas had apparently been liberated during its formation.

The nitrous oxide remaining, was not quite equal to seven measures; hence, at least four measures of it had been absorbed.

To ascertain the nature of the residuum, it was necessary to transfer it into another vessel, but this I found very difficult to accomplish, on account of the coagulated blood. By piercing through the coagulum and removing part of it by means of curved iron forceps, I at last contrived to introduce about 4½ measures of the gas into a small cylinder, graduated to,25 cubic inches, in which it occupied of course, nearly 9 measures; when a little solution of strontian was admitted to these, it became very slightly clouded; but the absorption that took place did not more than equal half its bulk. Consequently, the quantity of carbonic acid evolved from the blood, or formed, must have been extremely minute.

On the introduction of pure water, a rapid absorption of the gas took place, and after agitation, not quite 3 measures remained. These did not _perceptibly_ diminish with nitrous gas; their quantity was too small to be examined by any other test; but there is reason to suppose that they were chiefly composed of nitrogene.

From this experiment, it appeared that nitrous oxide is absorbed when placed in contact with venous blood; at the same time, that a very minute quantity of carbonic acid and probably nitrogene is produced.

_c._ In another similar experiment when nearly half a cubic inch of nitrous oxide was absorbed by about a cubic inch and three quarters of fluid blood, the residual gas did not equal more than ⅛, the quantity absorbed being taken as unity. This fact induced me to suppose that the absorption of nitrous oxide by venous blood, was owing to a simple solution of the gas in that fluid, analogous to its solution in water or alcohol.

To ascertain if nitrous oxide could be expelled from blood impregnated with it, by heat; I introduced to 2 cubic inches of fluid blood taken from the medial vein, about,6 cubic inches of nitrous oxide. After agitation, in seven minutes nearly,4 were absorbed. In ten minutes, after the blood had completely coagulated, the cylinder containing it, was transferred in contact with mercury, into a vessel of solution of salt in water; this solution was heated and made to boil. During its ebullition, the whole of the blood became either white or pale brown, and formed a solid coherent mass; whilst small globules of gas were given out from it. In a few minutes, about,25 of gas had collected. After the vessel had cooled, I attempted to transfer this gas into a small graduated jar in the mercurial apparatus, but in vain; the mass in the jar was so solid and tough, that I could not remove it. By transferring it to the water apparatus, I succeeded in displacing enough of the coagulum to suffer the water to come in contact with the gas; an absorption of nearly half of it took place; hence, _I conjecture_, that nitrous oxide had been given out by the impregnated blood.

_d_. Some fresh dark coagulum of venous blood, was exposed to nitrous oxide. A very slight alteration of color took place at the surface of the blood, perceptible only in a strong light, and a minute quantity of gas was absorbed. A taper burnt in the remaining gas as brilliantly as before, hence, it had apparently suffered no alteration.

_e_. To compare the physical changes effected in the venous blood by nitrous oxide, with those produced by other gases, I made the following experiments.—I filled a large phial, containing near 14 cubic inches, with blood from the vein of the arm of a man, and immediately transferred it to the mercurial apparatus. Different portions of it were thrown into small graduated cylinders, filled with the following gases: nitrogene, nitrous gas, common air, oxygene, nitrous oxide, carbonic acid, and hydrocarbonate.

The blood in each of them was successively agitated till it began to coagulate; and making allowances for the different periods of agitation, there was no marked difference in the times of coagulation.

The color of the coagulum in every part of the cylinder, containing nitrogene, was the same very dark red. When it was agitated so as to tinge the sides of the jar, it appeared exactly of the color of venous blood received between two surfaces of glass; no perceptible absorption of the gas had taken place.

The blood in nitrous gas was dark, and much more purple on the top than that in nitrogene. When agitated so as to adhere to the jar as a thin surface, this purple was evidently deep and bright. An absorption of rather more than ⅛ of the volume of gas had taken place.

The blood in oxygene and atmospheric air, were of a much brighter tinge than that in any of the other gases. On the top, the color was vermilion, but no perceptible absorption had taken place.

The coagulum in nitrous oxide, when examined in the mass was dark, and hardly distinguishable in its color from venous blood; but when minutely noticed at the surface where it was covered with serum, and in its diffusion over the sides of the jar, it appeared of a fine purple red, a tinge brighter than the blood in nitrous gas. An absorption had taken place in this cylinder, more considerable than in any of the others.

In carbonic acid, the coagulum was of a brown red, much darker than the venous blood, and a slight diminution of gas had taken place.

In the hydrocarbonate,[190] the blood was red, a shade darker than the oxygenated blood, and a very slight diminution of the gas[191] was perceptible.

[190] The hydrocarbonate employed, was procured from alcohol, by means of sulphuric acid. This gas contains more carbon, than hydrocarbonate from water and charcoal.

[191] The curious fact of the reddening of venous blood by hydrocarbonate, was discovered by Dr. Beddoes.

_f._ To human blood that had been saturated with nitrous oxide whilst warm and constantly agitated for four or five minutes, to prevent its uniform coagulation, oxygene was introduced; the red purple on the surface of it, immediately changed to vermilion; and on agitation, this color was diffused through it. On comparing the tinge with that of oxygenated blood, no perceptible difference could be observed. No change of volume of the oxygene introduced, had taken place; and consequently, no nitrous oxide had been evolved from the blood.

_g._ Blood, impregnated with nitrous gas, was exposed to oxygene; but after agitation in it for many minutes, no change of its dark purple tinge could be observed, though a slight diminution of the oxygene appeared to take place.

_h._ Blood that had been rendered vermilion in every part by long agitation in atmospheric air, the coagulum of which was broken and diffused with the coagulable lymph through the serum, was exposed to nitrous oxide; for some minutes no perceptible change of color took place; but by agitation for two or three hours, it evidently affirmed a purple tinge, whilst a a slight absorption of gas took place. It never however, became nearly so dark as venous blood that had been exposed to nitrous oxide.

_i._ Blood, oxygenated in the same manner as in the last experiment, the coagulum of which had been broken, was exposed to nitrous gas. The surface of it immediately became purple, and by agitation for a few minutes, this color was diffused through it. A slight diminution of the gas was observed. On comparing the tinge with that of venous blood that had been previously exposed to nitrous gas, there was no perceptible difference.

_k._ Blood exposed to oxygenated muriatic acid is wholly altered in its constitution and physical properties, as has been often noticed; the coagulum becomes black in some parts, and brown and white in others. Venous blood, after agitation in hydrogene or nitrogene, oxygenates when exposed to the atmosphere in the same manner as simple venous blood. I had the curiosity to try whether venous blood exposed to hydrogene, would retain its power of being oxygenated longer than blood saturated with nitrous oxide: for this purpose some similar black coagulum was agitated for some time in two phials, one filled with hydrogene, the other with nitrous oxide. They were then suffered to rest for three days at a temperature from about 56° to 63°. After being opened, no offensive smell was perceived in either of them, the blood in hydrogene was rather darker than at the time of their exposure, whilst that in nitrous oxide was of a brighter purple. On being agitated for some time in the atmosphere, the blood in nitrous oxide became red, but not of so bright a tinge as oxygenated venous blood. The color of the blood in hydrogene did not at all alter.

_l._ To ascertain whether impregnation with nitrous oxide accelerated or retarded the putrefaction of the blood; I exposed venous blood in four phials, the first filled with hydrocarbonate, the second with hydrogene; the third with atmospheric air, and the fourth with nitrous oxide. Examined after a fortnight, the blood in hydrogene and common air were both black, and stunk very much; that in hydrocarbonate was red, and perfectly sweet; that in nitrous oxide appeared purple and had no disagreeable smell.

In a second experiment, when blood was exposed for three weeks to hydrocarbonate and nitrous oxide, that in nitrous oxide was darker than before and stunk a little; that in hydrocarbonate was still perfectly sweet. The power of hydrocarbonate to prevent the putrefaction of animal matters, was long ago noticed by Mr. Watt.

_m._ Having accidentally cut one of my fingers so as to lay bare a little muscular fibre, I introduced it whilst bleeding into a bottle of nitrous oxide; the blood that trickled from the wound evidently became much more purple; but the pain was neither alleviated or increased. When however, the finger was taken out of the nitrous oxide and exposed to the atmosphere, the wound smarted more than it had done before. After it had ceased to bleed, I inserted it through water into a vessel of nitrous gas; but it did not become more painful than before.

From all these observations, we may conclude,

1st. That when nitrous oxide is agitated in fluid venous blood, a certain portion of the gas is absorbed; whilst the color of the blood changes from dark red to red purple.

2dly. That during the absorption of nitrous oxide by the venous blood, minute portions of nitrogene and carbonic acid are produced, either by evolution from the blood, or from a decomposition of part of the nitrous oxide.

3dly. That venous blood impregnated with nitrous oxide is capable of oxygenation; and vice versa; that oxygenated blood may be combined with nitrous oxide.

When blood separated into coagulum and serum, is exposed to nitrous oxide, it is most probable that the gas is chiefly absorbed by the serum. That nitrous oxide however is capable of acting upon the coagulum, is evident from _d._ In the fluid blood, as we shall see hereafter, nitrous oxide is absorbed by the attractions of the whole compound.

III. _Of the changes effected in Nitrous Oxide by Respiration._

To ascertain whether the changes effected in nitrous oxide by the circulating blood acting through the moist coats of the pulmonary veins of living animals, were highly analogous to those produced in it by fluid venous blood removed from the vessels, I found extremely difficult.

I have before observed, that when animals are made to respire nitrous oxide, a certain absorption of the gas always takes place; but the smaller animals, the only ones that can be experimented upon in the mercurial apparatus, die in nitrous oxide so speedily and occasion so slight a diminution of gas, that I judged it useless to attempt to analise the residuum of their respiration, which supports flame as well as pure nitrous oxide, and is chiefly absorbable by water.

In the infancy of my researches, I often respired nitrous oxide in a large glass bell, furnished with a breathing tube and stop-cock, and poised in water saturated with the gas.

In two or three experiments in which the nostrils being closed after the exhaustion of the lungs, the gas was inspired from the bell and respired into it, a considerable diminution was perceived, and by the test of lime water some carbonic acid appeared to have been formed; but on account of the absorption of this carbonic acid by the impregnated water, and the liberation of nitrous oxide from it, it was impossible to determine with the least accuracy, the quantities of products after respiration.

About this time likewise, I often examined the residuum of nitrous oxide, after it had been respired in silk bags. In these experiments when the gas had been breathed for a long time, a considerable diminution of it was observed, and the remainder extinguished flame and gave a very slight diminution with nitrous gas. But the great quantity of this remainder as well as other phænomena, convinced me that though the oiled silk was apparently air-tight when dry, under slight pressure, yet during the action of respiration, the moist and warm gas expired, penetrated through it, whilst common air entered through the wetted surface.

To ascertain accurately, the changes effected in nitrous oxide by respiration, I was obliged to make use of the large mercurial airholder mentioned in Research I. of the capacity of 200 cubic inches. The upper cylinder of it was accurately balanced so as to be constantly under the pressure of the atmosphere. To an aperture in it, a stop-cock having a very large orifice was adapted, curved and flattened at its upper extremity, so as to form an air-tight mouth-piece.

By accurately closing the nose, and bringing the lips tight on the mouth-piece, after a few trials I was able to breathe oxygene or common air in this machine for two minutes or two minutes and half, without any other uneasy feeling than that produced by the inclination of the neck and chest towards the cylinder. The power of uniformly exhausting the lungs and fauces to the same extent, I did not acquire till after many experiments. At last, by preserving exactly the same posture after exhaustion of the lungs before the inspiration of the gas to be experimented upon, and during its compleat expiration, I found that I could always retain nearly the same quantity of gas in the bronchial vessels and fauces; the difference in the volume expired at different times, never amounting to a cubic inch and half.

By connecting the conducting pipe of the mercurial airholder, during the respiration of the gas, with a small trough of mercury by means of a curved tube, it became a perfect and excellent breathing machine. For by exerting a certain pressure on the airholding cylinder, it was easy to throw a quantity of gas after every inspiration or expiration, into tubes filled with mercury standing in the trough. In these tubes it could be accurately analised, and thus the changes taking place at different periods of the process ascertained.

Whenever I breathed pure nitrous oxide in the mercurial airholder, after a compleat voluntary exhaustion of my lungs, the pleasurable delirium was very rapidly produced, and being obliged to stoop on the cylinder, the determination of blood to my head from the increased arterial action in less than a minute became so great, as often to deprive me of voluntary power over the muscles of the mouth. Hence, I could never rely on the accuracy of any experiment, in which the gas had been respired for more than three quarters of a minute.

I was able to respire the gas with great accuracy for more than half a minute; it at first, rather increasing than diminishing the power of volition; but even in this short time, very strong sensations were always produced, with sense of fulness about the head, somewhat alarming; a feeling which hardly ever occurs to me when the gas is breathed in the natural posture.

In all the numerous experiments that I made on the respiration of nitrous oxide in this way, a very considerable diminution of gas always took place; and the diminution was generally apparently greater to the eye during the first four or five inspirations.

The residual gas of an experiment was always examined in the following manner. After being transferred through mercury into a graduated cylinder, a small quantity of concentrated solution of caustic potash was introduced to it, and suffered to remain in contact with it for some hours; the diminution was then noted, and the quantity of gas absorbed by the potash, judged to be carbonic acid. To the remainder, twice its bulk of pure water was admitted. After agitation and rest for four or five hours, the absorption by this was noticed, and the gas absorbed considered as nitrous oxide. The residual unabsorbable gas was mingled over water with twice its bulk of nitrous gas; and by this means, its composition, whether it consisted wholly of nitrogene, or of nitrogene mingled with small quantities of oxygene, ascertained.

From a number of experiments made at different times on the respiration of nitrous oxide, I select the following as the most accurate.

E. 1. At temperature 54°, I breathed 102 cubic inches of nitrous oxide, which contained near ¹/₅₀ common air, for about half a minute, seven inspirations and seven expirations being made. After every expiration, an evident diminution of gas was perceived; and when the last full expiration was made, it filled a space equal to 62 cubic inches.

These 62 cubic inches analised, were found to consist of

Carbonic acid 3,2 Nitrous oxide 29,0 Oxygene 4,1 Nitrogene 25,7 ———— 62,0 ————

Hence, accounting for the two cubic inches of common air previously mingled with the nitrous oxide, 71 cubic inches had disappeared in this experiment.

In the last respirations, the quantity of gas was so much diminished, as to prevent the full expansion of the lungs; and hence the apparent diminution was very much less after the first four inspirations.

E. 2. At temperature 47°, I breathed 182 cubic inches of nitrous oxide, mingled with 2½ cubic inches of atmospheric air, which previously existed in the airholder, for near 40 seconds; having in this time made 8 respirations. The diminution after the first full inspiration, appeared to a by-stander nearly uniform. When the last compleat expiration was made, the gas filled a space equal to 128 cubic inches, the common temperature being restored. These 128 cubic inches analised, were found to consist of

Carbonic acid 5,25 Nitrous oxide 88,75 Oxygene 5,00 Nitrogene 29,00

Consequently, in this experiment, 93,25 cubic inches of nitrous oxide had disappeared.

In each of these experiments, the cylinder was covered with condensed watry vapor exactly in the same manner as if common air had been breathed in it. It ought to be observed that, E. 1. was made in the morning, four hours and half after a moderate breakfast; whereas, E. 2. was made but an hour and quarter after a plentiful dinner; at which near three fourths of a pint of table-beer had been drank.

From these experiments we learn, that nitrous oxide is rapidly absorbed by the venous blood, through the moist coats of the pulmonary veins. But as after a compleat voluntary exhaustion of the lungs, much residual air must remain in the bronchial vessels and fauces, as appears from their incapability of compleatly collapsing, it is evident that the gas expired after every inspiration of nitrous oxide mast be mingled with different quantities of the residual gas of the lungs;[192] whilst after a complete expiration, much of the unabsorbed nitrous oxide must remain as residual gas in the lungs. Now when a complete expiration is made after the breathing of atmospheric air, it is evident that the residual gas of the lungs consists of nitrogene,[193] mingled with small portions of oxygene and carbonic acid. And these are the only products found after the respiration of nitrous oxide.

[192] By lungs, I mean in this place, all the internal organs of respiration.

[193] Because these products are formed during the respiration of common air.

To ascertain whether these products were partially produced, during the process of respiration, as I was inclined to believe from the experiments in the last section, or whether they were wholly the residual gases of the lungs, I found extremely difficult.

I at first thought of breathing nitrous oxide immediately after my lungs had been filled with oxygene; and to compare the products remaining after the full expiration, with those produced after a full expiration of pure oxygene; but on the supposition that oxygene and nitrous oxide, when applied together to the venous blood, must effect changes in it different from either of them separately, the idea was relinquished.

I attempted to inspire nitrous oxide, after having made two inspirations and a complete expiration of hydrogene; but in this experiment the effects of the hydrogene were so debilitating, and the consequent stimulation by the nitrous oxide so great, as to deprive me of sense. After the first three inspirations, I lost all power of standing, and fell on my back, carrying in my lips the mouth-piece separated from the cylinder, to the great alarm of Mr. Patrick Dwyer, who was noting the periods of inspiration.

Though experiments on successive inspirations of pure nitrous oxide might go far to determine whether or no any nitrogene, carbonic acid and oxygene were products of respiration, yet I distinctly saw that it was impossible in this way to ascertain their quantities, supposing them produced, unless I could first determine the capacity of my lungs; and the different proportions of the gases remaining in the bronchial vessels after a compleat expiration, when atmospheric air had been respired.