have on the temperature of an animal under the circumstances of the last experiment, independently of any chemical action on the blood: since, if no chemical changes were produced, the circulation could not be maintained, and if the circulation ceased, the cooling properties of the air must be more confined to the thorax, and not communicated in an equal degree to the more distant parts. The following experiment, however, was instituted as likely to afford a nearer approximation to the truth, than any other that could be devised. move this. Exp. 8. I procured two rabbits of the same size and Exp. 8. At. colour: the temperature of the room was 64°. I killed tempt to reone of them by dividing the spinal marrow, and imme-, diately, having made an opening into the left side of the thorax, I tied a ligature round the base of the heart, so as to stop the circulation. The wound in the skin was closed by a suture. An opening was then made into the trachea, and the apparatus for artificial respiration being fitted into it, the lungs were inflated, and then allowed to collapse as in the former experiment, about 36 times in a minute. This was continued for an hour and a half, and the temperature was examined at different periods. The temperature of the room being the same, I killed the second rabbit in the same manner, and measured the temperature at corresponding periods. The comparative temperature of the two dead animals, under these circumstances, will be seen in the following table. No animal heat In this last experiment, as may be seen from the above apparently pro- table, the difference in the temperature of the two rabbits, duced by respiration. similar results. at the end of an hour and a half in the rectum, was half a degree, and in the thorax two degrees and a half; whereas, in the preceding experiment, at the end of an hour and forty minutes, the difference in the rectum was 24 degrees, and in the thorax 3 degrees. It appears, therefore, that the rabbit in which the circulation was maintained by artificial respiration cooled more rapidly on the whole, than the rabbit whose lungs were inflated in the same manner after the circulation had ceased. This is what might be expected if no heat was produced by the chemical action of the air on the blood; since in the last case the cold air was always applied to the same surface, but in the former it was applied always to fresh portions of blood, by which its cooling powers were communicated to the more distant parts of the body. In the course of the experiments which I have related, I was much indebted to several members of the Society for promoting the Knowledge of Animal Chemistry, for many important suggestions, which have assisted me in prosecut ing the inquiry. Mr. Home, at my request, was present at the seventh experiment. Dr. E. N. Bancroft was present at, and assisted me in the second experiment: and Mr. William Brande lent me his assistance in the greater part of those which were made. I have been farther assisted in making the experiments by Mr. Broughton, surgeon of the Dorsetshire regiment of militia, and Mr. Richard Rawlins, and Mr Robert Gatcombe, students in surgery. Many other exI have selected the above from a great number of similar periments gave experiments, which it would be needless to detail. It is sufficient to state, that the general results were always the same; and that, whether the pulse was frequent or slow, full, or small, or whether the respirations were frequent or otherwise, there was no perceptible difference in the cooling of the animal. General con clusions. From the whole we may deduce the following conclusions: 1. The influence of the brain is not directly necessary to the action of the heart. 2. When 2. When the brain is injured or removed, the action of the heart ceases, only because respiration is under its influence, and if under these circumstances respiration is arficially produced, the circulation will still continue. 3. When the influence of the brain is cut off, the secretion of urine appears to cease, and no heat is generated; notwithstanding the functions of respiration and the circulation of the blood continue to be performed, and the usual changes in the appearance of the blood are produced in the lungs. 4. When the air respired is colder than the natural temperature of the animal, the effect of respiration is not to generate, but to diminish animal heat. Addition to the Croonian Lecture for the Year 1810. (P.207.) duces similar blood with natural. In the experiments above detailed, where the circulation Artificial rewas maintained by means of artificial respiration after the spiration pro head was removed, I observed that the blood, in its pas- changes on the sage through the lungs, was altered from a dark to a scarlet colour; and hence I was led to conclude, that the action of the air produced in it changes analogous to those, which occur under ordinary circumstances. I have lately, with the assistance of my friend Mr. W. Brande, made the following experiment, which appears to confirm the truth. of this conclusion. show this. An elastic gum bottle, having a tube and stop-cock con- Experiment to nected with it, was filled with about a pint of oxigen gas. The spinal marrow was divided in the neck of a young rabbit, and, the blood vessels having been secured, the head was removed, and the circulation was maintained by inflating the lungs with atmospheric air for five minutes, at the end of which time the tube of the gum bottle was inserted into the trachea, and carefully secured by a ligature, so that no air might escape. By making pressure on the gum bottle, the gas was made to pass and repass into and from the lungs about thirty times in a minute. At first, the heart acted one hundred and twenty times in a minute, with regularity and strength; the thermometer, in the rectum, rose to 100°. At the end of an hour, the heart acted as frequently as before, but more feebly VOL. XXIX.-SUPPLEMENT. in the arteries was very little more florid than that in the veins; the thermometer in the rectum had fallen to 93°. The gum bottle was then removed. On causing a stream of the gas, which it contained, to pass through lime water, the presence of carbonic acid was indicated by the liquid being instantly rendered turbid. The proportion of carbonic acid was not accurately determined; but it appeared to form about one half of the quantity of gas in the bottle. B. C. BRODIE. iron by hidrogen gas. IX. Notes by Mr. J. H. HASSENFRATZ on the Disoxidation of Disoxidation of DESIROUS of repeating the experiment of Messrs. Priestley, Chaussier, and Amadeus Berthollet, on the disoxidation of iron by hidrogen gas, I last year employed Mr. Charbaut, then a pupil of the School of Mining, to make the experiment in my presence. He proceeded in two ways: in one the iron was disoxidated by hidrogen, in the other by oil and charcoal. In the latter experiment the metal was fused by increasing the temperature, so as to obtain a button of iron. More weight The experi On comparing these two modes, I was astonished to find, lost than in the that the diminution of weight of the oxidule of iron by hireduction by oil and charcoal. drogen was always greater than that effected by oil and charcoal. The perplexity into which I was thrown by these results induced me to repeat the experiment anew. Ac ments repeated. cordingly this year I employed at the Practical School of Mining the pupil Desroches, of whose sagacity and precision I was previously satisfied, to decompose by the action of hidrogen gas oxidules of iron from the valley of Aoste, and specimens of oligist iron from Elba, while other pupils assayed the same minerals before me in the dry way. The results obtained agreed precisely with those of last year. * Ann. de Chim, vol. lxi, p. 147. Finally Finally, at my departure from Moutiers, I requested the pupil Desroches to make fresh experiments on the decomposition of the oxidule of iron of Cogne, and oligist iron of Elba. The official statement of these experiments, certified by engineer Leboullenger, I shall proceed to lay before the public. Experiments on the Disoxidation of Oxide and Oxidule of Iron. It has been said, that all metals are capable of being dis- Disoxidation of oxidated by heat, and that the temperature required for metals by heat. their reduction is much higher than that of their oxidation. It is easy to conceive, that, if the tendency to take the aeriform state be less powerful than the attraction of the oxigen by the metal, the oxigen will be solidified, and an oxide formed: but if the elasticity be superior to the attraction, no combination, or oxidation, will take place. This occurs in the manufacture of minium: too strong a fire produces massicot, and sometimes reduces the oxide entirely. It is observable too, that, beyond a certain tem- Oxidation by perature, the time required for oxidation is in the inverse heat. ratio of the heat. This I had an opportuity of observing in the oxidation of iron by heat last year. Having taken some pure filings of good iron, and exposed them to a graduated heat, I obtained in a very little time an addition of 32 per cent: I increased the heat and the current of air, but it was a long while before I gained 40 per cent: and it was not without a great deal of trouble, and a very long time, that I obtained the known result of 45 per cent, which I could not exceed. heat? But is heat alone capable of reducing all metals? This Are all metal question is already decided with respect to some, which reducible by have but a feeble attraction for oxigen. As to those which retain it forcibly, it may be, that the heat requisite for their disoxidation is superior, or at least equal to that necessary for their fusion; and then it would be impossible to separate the gas from the metal. But if a powerful disoxidizer be employed in conjunction with caloric, so great a heat will not be required to reduce the metal: this no doubt induced the younger Mr. Berthollet Bb 2 |