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capacity of eight liquid ounces, was selected and carefully enveloped in bad conducting substances, viz. several folds of flannel, of fine oiled paper, and of oiled cloth. Thus prepared, and a perforated cork being provided holding a delicate thermometer, 2 cubic inches of mercury were introduced, and immediately after it was filled with venous blood kept liquid as before described. The vial was now corked and shaken; the thermometer included was stationary at 45°. After five minutes that it was so stationary the thermometer was withdrawn; the vial, closed by another cork, was transferred to a mercurial bath, and 14 cubic inch of oxygen was introduced. The common cork was returned, and the vial was well agitated for about a minute: the thermometer was now introduced; it rose immediately to 46°, and, continuing the agitation, it rose further to 46°.5, very nearly to 47°. This experiment was made on the 12th of February, 1838, on the blood of the sheep. On the following day a similar experiment was made on the venous blood of man. The vial was filled with 11 cubic inches of this blood, its fibrine broken up in the usual manner, and with 3 cubic inches of mercury; the temperature of the blood and mercury was 42°-5, and the temperature was the same after the introduction of 3 cubic inches of oxygen. The temperature of the room being 47°, a fire having shortly before been lit, the vial was taken to an adjoining passage, where the temperature of the air was 39°. Here the vial was well agitated, held in the hand with thick gloves on as an additional protection; after about three quarters of a minute the thermometer in the vial had risen a degree, viz. to 43°-5." Dr. Davy relates two other experiments, of which the first was performed on the venous blood taken from the jugular vein of a sheep, the second on arterial blood. The three experiments with venous blood showed that when agitated with mercury and air for the space of a minute, venous blood was heated to the extent of 1° Fahr., whilst the arterial blood was heated only half a degree.

Dr. Davy quotes Sir Charles Scudamore, who, in his Essay on the Blood,' at p. 59, states that venous blood cools much more slowly in oxygen gas than in atmospheric air; that the same blood divided into two cupping-glasses, "after an interval of eight minutes from the beginning of the experiment," exhibited a difference of 8°,—that exposed to oxygen being 85°, that to atmospheric air 77°.

H. Nasse, in his article on Animal Heat in the fourth volume of Wagner's 'Handwörterbuch der Physiologie' (1842), quotes Marchand to the effect that when oxygen is shaken with blood the latter is heated.

In a paper entitled "On the Relative Temperature of Arterial and Venous Blood," Mr. W. B. Savory, having described at considerable length observations on the temperature of the two sides of the heart, describes others performed with a view to check the accuracy of the experiments of Dr. John Davy, and states the conclusions to which he was led by his own experiments, viz.:-1st, that when venous blood is treated, as was done by Dr. Davy in his experiments, with oxygen, its temperature was usually raised from 1° to 140 or 2°; 2ndly, that when venous blood was treated in a similar manner with hydrogen or carbonic acid, its temperature was as frequently raised, and generally to the same extent; 3rdly, that similar experiments upon arterial blood usually yielded the same results; 4thly, that in all cases the increase of temperature seemed to be the result of the agitation. In concluding his paper, Mr. Savory remarked, "At present there is no evidence upon which we can safely venture further into this inquiry. If, as I conclude from my experiments, arterial blood is warmer than venous, the increase of temperature must occur in the lungs as a result of those changes

which the blood there undergoes. Of the nature of those changes, little or nothing is known."

In my early researches, conducted during the months of May and June 1869, I had attempted to determine, by means of comparatively simple contrivances, whether any heat was evolved during arterialization, making use of delicate thermometers. At first I used a glass bottle furnished with a tubulature, near the bottom in which a cork, perforated and furnished with a glass tube closed by india-rubber tubing and a clip, was inserted. The neck of the bottle was furnished with a cork perforated in two places; through one of the perforations a delicate Centigrade thermometer passed into the centre of the flask, whilst into the other was inserted a bent glass tube through which gas might be introduced into the apparatus. The bottle which I have described was filled with venous blood, both the tubes communicating with its interior being closed. It was then maintained at a temperature varying between 30° and 35° C. for many hours, until it had assumed the characteristic cherry-red coloration which indicates the complete removal of the loosely combined oxygen of the blood. The apparatus having been allowed to cool, it was invested with a jacket of felt. An india-rubber tube was made to connect the upper glass tube with a hydrogen gasometer, whilst the lower tube being opened, the hydrogen expelled any required quantity of blood. The apparatus was then shaken and the temperature determined. Then by a repetition of the process (followed in the introduction of hydrogen) pure oxygen gas was made to displace more of the blood, and the process of shaking repeated as before. The results of such experiments were eminently unsatisfactory, varying obviously with the amount of mechanical work which was formed by the experiments, and which yet did not admit of exact determination.

In some experiments I observed a heating which amounted to 0°-3 C.; in other cases the difference in the readings, before the introduction of oxygen and after it, seemed to point to a cooling instead of to a heating. To give an idea of the indefinite and perplexing results which I obtained, I shall cite the details of an experiment performed on the 23rd of June, 1870, by Professor Tait and myself, the apparatus used being a tin vessel resembling in principle the one of glass which I have already described. This vessel was covered with felt, and, when shaken, it was held by means of a very strong iron clamp. Having been filled with sheep's blood, it was placed in an air-oven and maintained for a period of twelve hours at a temperature which oscillated between 100° and 110° Fahr. It was afterwards placed in the room in which my experiments were carried on; but in order to make it cool more rapidly, its felt covering was taken off, and it was placed in water at a temperature of 15° C. It was dried, again covered with felt, and fixed in its clamp. Hydrogen was then made to expel 4.5 cubic inches of blood, which was found by spectroscopic examination to exhibit the single band of reduced hæmoglobin; after shaking the blood and hydrogen. in the apparatus, its temperature was found to be 17°.8 C., then 18° C., the temperature of the air being 20°-4 C. 10 cubic inches of blood were then drawn off and replaced by oxygen, which was brought in contact with the blood by shaking; the temperature rose to 18°.1 C.: more oxygen was introduced and the shaking repeated, the temperature rising to 18°.25, 18°4, 18°.5, 18°.6, 18°.6, 18°.55, 187, 18°.75, 18°.77. At the conclusion of the experiment the quantity of blood which had been arterialized was found to be 360 cubic centims. This experiment merely gave one of many results; for as long as I followed this method I was quite unable twice to determine the same

amount of heat as the result of oxygenation of the blood. The amount of heating in a given time depended upon several important factors, as the difference between the temperature of the blood in the experimental vessel and that of the surrounding air, upon the amount of blood contained in the apparatus, and the space through which the vessel was moved during its agitation, no less than upon the number of the agitations.

To describe, or even to give the results of a series of experiments so eminently unsatisfactory, would be a mere waste of time; it will be sufficient for me to state, however, that I clearly came to the conclusion that, like those who had preceded me, I had obtained no positive proof of the heating of blood when it absorbs oxygen, there having been as great a heating when water as when blood was experimented upon.

In commencing new experiments this year, I did so with the conviction that, in order to obtain results of any value, my apparatus should be so constructed and my experiments so conducted as to preclude the possibility of any appreciable rise in temperature resulting from the mechanical work of shaking. Then I decided upon discarding thermometers, and making use of thermo-electric junctions of great delicacy.

The galvanometer employed in the research was one resembling one of Sir Wm. Thomson's older forms, constructed especially for Professor Tait, every possible precaution having been taken to avoid a trace of iron in the coils and framework. The wire was drawn through agate plates from electrolytic copper, covered with white silk and formed into four coils, each adjusted to produce the maximum effect with the least resistance, those parts of the coils nearest the magnets being made of finer wire. The astatic system vibrated under the earth's force once in eight seconds; but as this was much too delicate for my purpose, I placed near the instrument a bar-magnet, which reduced the period of vibration to 3.4.

The thermo-electric junctions which I employed were made by twisting very thin iron and copper wire together, the free ends of the copper wires being immersed into the mercury pools of a very simple form of commutator placed in the circuit, which enabled me, with the greatest ease, to reverse the current flowing along the wires.

The apparatus actually employed in my experiments consisted of an upper glass vessel, which I may call the blood reservoir, to which was connected a lower vessel, also of glass, and in which the blood, which was the subject of experiment, could be brought in contact with the gases which were intended to act upon it.

The upper vessel was a glass bulb of a pyriform shape, and had a capacity of about 150 cubic centimetres. Above and below it was drawn out, so as to present two tubes, the upper of which was bent at right angles and furnished with a piece of india-rubber tubing, which admitted of being closed by a clamp, whilst the lower was furnished with a very accurately ground stopcock. In the side of the bulb was a round tubulature, which could be closed with a cork, through which passed a thermo-electric junction. The lower, or mixingvessel, was cylindrical in shape, and possessed four apertures. The upper one was closed by a cork, bored so as to allow of the passage of a glass tube, attached above by means of an elastic tube to the stopcock of upper vessel or reservoir, and made of such a length as to reach to the bottom of the mixingvessel. Near the upper aperture was a second lateral one, into which a glass tube had been fused. This glass tube could be connected, by means of a metallic tube and stopcocks, either with a Sprengel mercurial aspirator or with an oxygen or hydrogen gasometer. A third lateral aperture was

closed with a cork, perforated (like the one which closed the upper vessel) by a second thermal junction. A fourth aperture in the mixing-vessel, closed by a stopcock, enabled it to be emptied.

In determining with such an apparatus whether heat is generated when venous blood becomes arterial, the upper vessel is disconnected from the lower at a point below the glass stopcock previously described; it is completely filled with water, and then the water is displaced by a stream of pure hydrogen gas admitted through the upper tube.

The lower glass tube is then connected with the vessel which contains the blood to be experimented upon. The upper tube, through which hydrogen had been admitted, is now connected to the Sprengel pump, which rapidly sucks the blood into the vessel, without the slightest possibility of its coming in contact with oxygen. The upper vessel is either partially or completely filled with blood, but it always is ultimately left in connexion with a hydrogen gasometer.

The mixing-vessel (the lowest aperture of which has been closed by indiarubber tubing and clip) is now connected to the Sprengel pump, and a vacuum is formed into which hydrogen is allowed freely to flow. The vacuum is renewed three or four times consecutively, hydrogen being allowed to flow into the apparatus each time. The object of this is to exclude traces from the lower vessel of atmospheric oxygen.

The stopcock which connects the upper and lower vessels is opened, and venous blood is allowed to flow into the lower vessel. In actual work both the upper and lower vessels are thickly covered with wadding. The upper one is firmly fixed in a clamp, and constitutes a reservoir, which, except when the atmospheric changes in temperature are abnormally sudden, maintains during limited periods of time a constant temperature. The lower tube being connected to the stopcock of the upper by means of a flexible indiarubber tube, admits of being completely tilted, or, if necessary, shaken.

As soon as the lower vessel contains the blood to be experimented upon, the thermal junctions are brought in connexion with the galvanometer. The amount of deviation on the graduated scale, and the direction of the deviation, at once tells the experimenter whether the upper or the lower junction be the hotter. The lower vessel is thoroughly shaken, then, after some time, the temperature of its contents is determined by reading on the scale placed in front of the galvanometer. The tube and its contents are then repeatedly tilted, a reading of the galvanometer being taken after each set of five tilts. After a certain time the lower vessel has assumed a constant temperature, and readings, at the interval of two or three minutes, show no perceptible change. I may remark that the galvanometer which, through the kindness of Prof. Tait, was placed at my disposal was so set that in my various experiments one division of the divided scale corresponded to the 100th or the 120th of a degree Cent. The first observations made with my apparatus were intended to determine whether such an amount of agitation as would be required to communicate a thoroughly arterial colour to perfectly venous blood would heat the fluid to a perceptible extent, in consequence of the mechanical work expended in the agitation.

In preliminary experiments I found that venous blood assumed a beautiful arterial hue, when it was mixed with oxygen contained in the mixingvessel, by successively tilting the tube twenty times. In each tilt the tube containing blood and oxygen was completely reversed. In other preliminary experiments I found that when the tube contained thoroughly arterialized blood or water, the process of tilting had no influence on the

temperature of the contained fluid. It was, therefore, obvious that any heating which might occur in the process of tilting or shaking in subsequent experiments could not be referred to the mechanical work expended in the tube and its contents.

My next experiments consisted in determining whether, when agitated with a neutral gas, as, for example, hydrogen, any material change in the temperature of the blood occurred; they led to the result that when agitated with hydrogen gas no heating of the blood results, it being always remembered that the mechanical agitation to which the blood and the neutral gas were subjected was the same as in my experiments with blood and oxygen.

In my systematic experiments on the heat generated during the process of arterialization, the following observations were always made:

1. The temperature of the lower as contrasted with the upper vessel was determined after the latter had been exhausted.

2. The temperature-observations were repeated after shaking with hydrogen.

3. After the renewal of a vacuum.

4. After admission of oxygen in the mixing-vessel.

5. After oxygen had been thoroughly shaken with the blood.

The results of my experiments on very numerous samples of venous blood have led to the conclusion that whilst, as I have previously mentioned, no heat is evolved on agitating blood with hydrogen, there is, on agitation withoxygen, always a slight evolution of heat.

To determine the exact heating, when venous blood of varying gaseous composition is arterialized, appears to be most desirable. We should especially attempt to determine the heating observed when the average venous blood contained in the right ventricle and directly drawn from it is arterialized. The first and most important datum to be ascertained appeared to me, however, to be the heating which takes place when blood which has been thoroughly reduced, i. e. which contains no loosely combined oxygen and exhibits Stokes's spectrum, is completely arterialized.

From five sets of experiments on the heat developed during the arterialization of perfectly reduced blood, I arrived at the conclusion that the mean rise of temperature during the absorption of oxygen amounted to 0°-0976 C. The maximum heating found was 0°-111 C., and the minimum 0°.083 C.

The research, of which the above are the results, was conducted in the Physical Laboratory of the University of Edinburgh; and I have to express my thanks to Professor Tait for the uniform kindness with which he helped me by advice, assistance, and apparatus in ascertaining the facts which are recorded in this Report. I intend to extend these researches very greatly. It is most desirable that in future experiments venous blood of known composition be employed, and that the amount of oxygen absorbed and CO, evolved be ascertained after each experiment. I propose likewise to increase the period during which the blood is agitated, making use of an arrangement whereby the mechanical work performed in the agitation may be precisely. determined.

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