ANIMAL HEAT. 



657 



We 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, 

 are 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. 



at the temperature of 42 c. (108 F.) for fifteen 

 minutes, the temperature of the muscle as compared 

 with that of the other was found to have increased one- 

 fifth of a degree. When the whole body was plunged 

 iu a hot bath at the temperature of 49 c. (120 P F ), 

 the deviation of the needle varied from 12 to 13 

 and 14 of its scale, which indicated a rise in tem- 

 perature of from one- fifth to two-fifths of a degree c. 

 The pulse was increased to 112 beats per minute, 

 the body being immersed in this bath. The tempe- 

 rature of the body before immersion was 36, 70 c. 

 (98 F.), a degree to which it immediately returned 

 after coming out of the bath. In trying experi- 

 ments of the same kind subsequently, but with 

 baths at a somewhat lower temperature, namely, 

 42, 50 (109 F.), no rise of temperature was indi- 

 cated. The immersion in these cases was not con- 

 tinued for more than twenty minutes. Had it been 

 protracted for a longer time, the result might have 

 been different. When a doe, whose muscles indi- 

 cated a temperature of 38, 50 (102 F.), was 

 plunged into a hot bath at 49 c. (120 F.), the 

 temperature rose rapidly by half a degree, a degree, 

 and finally two degrees c. ; but the animal had be- 

 come so much enraged that it was found necessary 

 to take him out of the water. The needle of the 

 apparatus being passed into the chest, a like rise in 

 temperature was indicated ; but ihe rise in tempe- 

 rature was found to happen principally when the 

 animal became angry ; and it is doubtful how far 

 the state of exasperation influenced the results. 



In one experiment the one needle being passed 

 into the biceps muscle of a young man, the other 

 into the long radial supinator of a man aged forty- 

 five, no sensible deviation of the magnetic indicator 

 ensued. A vein was then opened in one of the 

 arms, as near as possible to the point at which the 

 needle had been introduced, but no change of tem- 

 perature took place either during or after the flow 

 of the blood. The common iliac artery of a dog 

 was now isolated and a ligature thrown loosely 

 round it, so that it could be compressed or left free 

 at pleasure, and one of the needles of the apparatus 

 plunged into the fleshy part of the thigh. The 

 current of blood having been interrupted, the tem- 

 perature of the limb began to fall, but not until 

 after the lapse of an interval of twenty minutes, 

 when it still amounted to no more than about half a 

 degree c. The free access of blood having been 

 restored, the temperature soon rose again to the 

 normal point. The effect, though trifling in this 

 case, and the same experiment was repeated several 

 times always with the same result, is still suffi- 

 cient to show that the arterial blood exerts a direct 

 influence upon the temperature of the animal tis- 

 sues. The effect, however, it is obvious from the 

 time which elapses before it becomes apparent, is 

 to be attributed, not to the blood which is circulating 

 in the trunks and branches of the vessels, but to 

 that which is contained in the vascular rete. ED.] 

 VOL. II. 



This fact is demonstrated in the most satis- 

 factory manner by the delicate experiments of 

 Messrs. Becquerel and Breschet as follows. 

 When one of the joinings (soudures) is kept 

 uniformly at a temperature of 36 c. (97 F.). 

 and the other is inserted into the biceps muscle 

 with the arm extended, the magnetic needle 

 was found to deviate about .10 of a degree. 

 On the arm being bent, however, the amount 

 of deviation was observed to increase suddenly 

 to the extent of from one to two degrees. 

 Waiting till the oscillation of the needle and 

 its return are completed, if the arm be bent 

 anew so as to give a fresh impulse to the needle 

 for several times in succession, a deviation of 

 fifteen degrees is obtained at length, equivalent 

 to a difference of five degrees in comparison 

 with the original deviation, and corresponding 

 to an increase of about half a degree of tem- 

 perature as measured by the centigrade scale. 

 If the needle be inserted into the biceps, and 

 the arm be used in the action of sawing for 

 about five minutes, the temperature is observed 

 to rise considerably, sometimes to the amount 

 of a degree centigrade. 



In these researches, then, we have evidence of 

 facts of which we could not have acquired any 

 precise information by our ordinary means of 

 investigation. Every one, indeed, knows that 

 exercise warms the body ; but every one also 

 sees that in producing this effect, besides the 

 contraction of the voluntary muscles, exercise 

 is accompanied by an acceleration in the mo- 

 tions of the heart and organs of respiration. 

 In this simultaneous concurrence of a variety 

 of phenomena, it was impossible to distin- 

 guish the share which each had in the general 

 result. Such an analysis could only be made 

 by an experiment of the delicate and ingenious 

 description of that which has been detailed. 



It would appear that it is by the repetition 

 of the muscular contraction after each relaxa- 

 tion that the highest evolution of heat is ob- 

 tained, each contraction producing a slight in- 

 crease of temperature, which, with the addition 

 of that which follows, mounts to a certain 

 limited point which it cannot pass. Let us 

 remark, however, that the mere persistence of a 

 primary contraction ought to have the effect of 

 causing or maintaining a temperature higher 

 than that which is evolved by a contraction 

 followed immediately by relaxation ; indeed it 

 is now known that a permanent muscular con- 

 traction is but a series and succession of smaller 

 and imperceptible contractions, following each 

 other with extreme rapidity. 



It were well to observe here, that neighbour- 

 ing parts must increase in temperature at the 

 same time much less in consequence of the 

 direct communication of heat in virtue of con- 

 tiguity than by the afflux of blood, which, 

 transmitted to the muscles in larger quantity, 

 must also be more copiously than usual dis- 

 tributed to adjacent tissues. The relaxation of 

 the muscles ought, on the other hand, to have 

 a tendency to reduce the temperature, and this 

 by so much the more as the relaxation is more 

 complete. From all this it follows that the 

 attitude and state of the bodv will be favoura- 



2 x 



