These considerations led to the adoption of thermoelectrical means by Messrs. Becquerel and Breschet. The processes they employed in procuring indications of temperature were the following. The only means we have of pe netrating into the interior of organs without in jury is to make use of a needle similar to that employed in acupuncture. Now it is easy to arrange this needle so as to obtain thermoelec tric indications, which proclaim immediately and with the greatest precision the temperature of the part or medium with which the point happens to be in contact. It is enough to compose this needle of two others in metal, two of the extremities of which are soldered together in a few points only, whilst the other two are placed in communication with one of the extremities of the wire of an excellent ther mo-electric multiplier. The slightest changes of temperature at the points of junction give origin to an electrical current, which, in reacting on the magnetic needle, causes it to deviate by a certain number of degrees, which conse quently become indices of the temperature of the point of the needle, and therefore of the medium in which it is placed. The multiplier ought to be so sensitive as to show a deviation of one degree of the magnetic needle for each one-tenth of a degree of temperature as mea sured by the centigrade scale, an amount of temperature made sensible by the union of the two ends of the wire which forms its circuit with an iron wire soldered by its ends.
So much for the general principle upon which and by which the inquiries of Messrs. Becquerel and Breschet were conducted. As to all the precautions necessary to render re searches of the kind fruitful, as these are nume rous, we beg to refer for an account of them to the memoir of the authors themselves.
Difference of temperature according to the depth.—By the means contrived by Becquerel and Breschet the temperature of the calf of the leg at the depth of four centimetres from the surface was found to be (about 98° F.), and at one centimetre (about F.), a difference of 2°,25 (4° F.). In the chest the temperature at the depth of the pectoralis major, compared with that of the superficial cellular tissue at the depth of one centimetre, showed a corresponding difference; the deeper parts were 2°,25 (about 4° F.) higher than the more superficial. In seven experiments made on the arm the mean difference of temperature between the deeper strata of the biceps and the superficial cellular tissue over the same muscle amounted to 1°,59 c. in favour of the deeper parts.
The next point of inquiry was toknow whether it was enough to penetrate to the depth of three or four centimetres into the trunk and limbs to attain the points of highest temperature in these parts. With tbis view we have compared the observations made by the authors mention ed, in the same individual, with regard to the temperature of the mouth and of the biceps muscle, and we find that the mean temperature of the mouth was that of the biceps (about F.),—a result which may be called identical with the former. The mean of seven other experiments, however, shows the relation of 36°,89 c. for the mouth, of c. for the biceps; the difference here is evidently in favour of the mouth. It were to be wished that inquiries in this direction were multiplied in order that absolute certainty may yet be attained.
In the preceding experiments, in penetrating to different depths, the nature of the tissues at tained also differs, a circumstance which must tend to complicate die results; for it is possi ble that the nature of the tissue may have some influence on the evolution of heat. This is even an inference which we should deduce from the principles already established, were it merely in consideration of the different quanti ties of blood they contain. And this conclu sion is even confirmed by the experiments of the parties mentioned ; for on compressing the humeral artery strongly, the motion of the nee dle immediately announced a fall of tempera ture to the extent of several tenths of a degree. This experiment is interesting from the rapidity and precision of the effect. There are other cases well known by which we are led to a corresponding conclusion ; but nowhere else is the fact seen in so simple a guise, or in so ma nifest a relation of cause and effect. In opera tions for aneurism, indeed, and other cases re quiring the ligature of a large artery, the tem perature of the parts supplied by the vessel tied falls so low as to require to be supported by artificial warmth ; hut then a severe and bloody operation has been performed by which the conditions are complicated. in the expe riment mentioned, on the contrary, nothing occurs to disturb the state of the economy ; the effect instantly follows the cause, and its amount is even at the same moment ascer tained.
Seeing, then, that in the same tissue the freer or more interrupted access of arterial blood causes the temperature to vary, it is fair to infer that the relative freedom of access or quantity of this fluid which circulates through other tissues should have an influence upon their temperature ; in other words, that tissues differ in their power of producing heat according to the quantity of blood which circulates through them. ‘Ve can scarcely doubt, therefore, but that the differences of temperature observed be tween the deeper and more superficial parts are complicated by the mere fact of difference of distance from the surface, and also by the cir cumstance of difference of tissue. The super ficial layer in the preceding experiments was cellular membrane ; the deeper layer was mus cular. But the muscles receive a much larger quantity of blood than the cellular membrane, and their temperature, from this circumstance alone, ought to be higher.* NVe might even deduce from this a fact of great importance in the animal economy, viz. that muscular contraction is a cause of heat, in asmuch as it determines the afflux of blood to wards the muscles themselves as well as to wards all the surrounding parts. It is very difficult to conceive an occasion of verifying this position in its simplicity ; for bodily efforts, in which the skin becomes red and injected, arc always accompanied with some disturbance of the respiration and motion of the blood. We have, however, had an opportunity of seeing one individual of athletic powers, who, by merely throwing the muscles of the fore-arm into strong contraction, could cause the integu ments of the forearm to become red. During the act of muscular contraction consequently, the temperature must have a tendency to rise.