Sept. 20, 1877] 



NATURE 



451 



This series of experiments proved that which was only indi- 

 cated in the ascents with a free balloon, viz., that the change of 

 temperature with increase of elevation has a diurnal range, 

 the change being the greatest at about midday and the early 

 afternoon hours, decreasing till about sunset, at which time, 

 when the sky was free from clouds, there was little or no change 

 of temperature up to the height of several hundred feet. I was 

 not able, by means of M. Giflard's balloon, to take any obser- 

 vations at about noon and early afternoon hours, nor any obser- 

 vations after sunset, as the balloon never ascended at these 

 times ; but such observations were greatly needed, as there 

 seemed to be at this time a very high probability that the tem- 

 perature of the air at night must increase with elevation. 



A thermometer was placed at the height of 22 feet, sufficiently 

 protected from the effects of radiation, and a second one at the 

 height of 4 feet, and eleven years' observations of these 

 instruments have been taken daily at 9 A.M. ; noon; 3 p.m. ; 

 and 9 P.M. 



These observations were reduced by taking the difference 

 between the readings of the two thermometers and affixing the 

 sign + to that difference when the temperature was higher at 

 the higher elevation ; and the sign — when lower. By taking 

 the mean differences for each month between the temperatures at 

 22 feet and 4 feet, it was found that at all hours of the day 

 during the months of January, February, November, and 

 December, in the afternoon hours of March, September, and 

 October, and night hours throughout the year, the sign was + 

 and that it was - at all other times, clearly indicating the fact 

 of an increase of temperature with increase of elevation during 

 the night hours throughout the year. 



THE HEAT PHENOMENA ACCOMPANYING 

 MUSCULAR ACTION 



'T'HE fact that in the living muscle heat always appears when 

 •* the muscle does work (Heidenhain having shown that of 

 two muscles equally weighted and undergoing equal contractions, 

 one doing external work, while the other does none, the former 

 gives out more heat than the latter), is an exception to the 

 general rule in mechanics, that heat disappears when work is 

 done. It is not, however, in contradiction to the general 

 principle of the conservation of energy, but shows that in the 

 living muscle, when stimulated to action, molecular processes 

 occur,' which, along with the doing of work, cause a development 

 of heat. The relation of the heat developed to the work done 

 had not been determined vritb any satisfactory accuracy, probably 

 owing to the want of sufiiciently delicate apparatus, though 

 it might naturally be expected to help to an understanding 

 of the phenomena. The subject has been taken up by M. 

 Nawalichin, who, favoured by the experimental means at hand 

 in M. Heidenhain's Physiological Institute, made a careful 

 examination of the development of heat in the active muscle. 

 The experiments were very difficult and tedious, and by reason 

 of the smallness of the values to be measured, required very 

 great foresight and care in the experimental arrangements. The 

 full account of this investigation is given in PJliigcr's Archiv. 



The first series of experiments bore on the question of the 

 production of heat when a particular muscle of the frog is 

 excited, through the nerve, by stimuli of increasing strength to 

 increasing contractions. As, during the experiments, the 

 excitability of the preparation varies, the relation to the strength 

 of stimulus was left out of account, and only the ratio between 

 development of heat and height of contraction examined. The 

 height of contraction was indicated graphically by the muscle 

 itself on a smoke-blackened plate. The development of heat 

 was measured by the deflection of a fine thermo-multiplier, and 

 the stimulation of the nerve was effected by accurately measurable 

 electric actions. The observations were only made when the 

 needle was entirely at rest, which was very difficult to secure, so 

 sensitive was the apparatus. 



The tabulated numbers from experiment show : (l) that the 

 sum of the tw vira, liberated in the muscle by increasing 

 stimuli, increases only so long as the lifting-heights (Hiibhohen) 

 increase. With a certain amount of stimulus when produced by 

 the sending of a constant current, the height of contraction 

 reaches a maximum, and therewith, too, the production of heat. 

 With a particular method of stimulation there is, under certain 

 conditions, a fresh increase of the amount of contraction above 

 the maximum amount, the so-called " supermaximal " contrac- 



tion ; where this occurred, the heat-production also rose. It 

 may therefore be said that in general the development of heat 

 increases with increased 'lifting-height, and decreases with 

 decreased lifting-height. 



The increase in heat-production, however, does not take place 

 proportionally to the increase in lifting- height, but in much 

 quicker ratio. Of this unexpected result M. Nawalichin assured 

 himself by repeated discussion of the numerical values obtained ; 

 Ijut he did not succeed in determining more precisely the law of 

 increase. 



This result led to the expectation that the same mechanical 

 work of a muscle would be accompanied by unequal heating 

 when the muscle raised a weight to the same height by several 

 small contractions, and when it raised it by one great contrac- 

 tion. In a great contraction more heat would become free than 

 in several small ones, the sum of which was equal to the great. 

 Experiments (though some were difficult) fully confirmed this, 

 especially after it was ascertained that the cooling during the 

 longer period of the several smaller contractions as against the 

 shorter duration of the great contraction, did not play a part. 



It is shown, then, that as the stimulation increases, the tem- 

 perature of the muscle, and accordingly the exchange of material, 

 increase in much quicker ratio than the n echanical work, and 

 that the stronger the stimulation the less favourable is the relation 

 of the exchange of material to the doing of work. 



These facts are in accordance, as M. Nawalichin points out, 

 with the common experience that the climbing of a hill is much 

 less heating and exhausting when we go zigzag than when we go 

 straight up. In the former case a greater number of small liftings 

 of the body result in the same doing of work as occurs in the 

 second case through a smaller number of great liftings. The 

 exchange of material, as the second series of experiments show, 

 must essentially be greater in the second case than in the first ; 

 and on the amount of it depends, on the one hand, the develop- 

 ment of heat, on the other the exhaustion. 



In order to get at the inner connection of the phenomena 

 observed, M. Nawalichin sought first to decide the question 

 whether the accelerated increase in production of heat was due to 

 the increase of the stimulus in itself or to the increase of the con- 

 traction produced by the increased stimulation. According to 

 Helmholtz's observations, whetj a muscle is subjected to two 

 maximum stimuli, one following close on the other, the second 

 stimulus produces an increase of contraction only when, at com- 

 mencement of the second contraction, the first has already 

 reached a considerable height. If this be not the case, as 

 happens if the interval of the two stimuli be less than ^juth of 

 a second, the two stimulations produce no greater contraction 

 than each alone. Now in what way does the production of heat 

 occur in this latter case ? Experiment showed that also with 

 double stimulation of the nerve, an increase of the heat-develop- 

 ment only occurred when it had as result an increase in the 

 height of contraction ; the increase of the stimulus in itself is 

 thus without influence on the amount of heat-production. Hence 

 the cause of the quicker increase of the heat-production. That 

 of the amomit of contraction must be sought in conditions 

 operative durmg the course of the contraction. 



To determine these conditions the author made experimental 

 inquiry into the relation of heat-development to the states of 

 tension of the muscle during the progress of contraction. He 

 found that the muscle developed less heat the less its tension 

 before action ; with which may be mentioned that this tension 

 of the muscle, weighted and stretched by the weight, is smaller 

 the more it has, through contraction, approximated to the 

 natural length. Experiments, also, as to the relation of the 

 heat-production to the change of state of tension during the act 

 of contraction showed an influence of this, such that in each 

 moment of action the quantity of heat depends on the tension. 

 This suggested the idea that the greater heat-production with 

 increasing stimulation is perhaps a consequence of the longer 

 duration of the stronger contraction. The experiments proved, 

 however, that this idea is not justified, for the muscle made small 

 and great contractions in the same time. 



As to the nature of the internal processes in the muscle, which 

 may be the basis of the phenomena observed, M. Nawalichin 

 offers the following remarks : — 



" We know that the contracting, muscle is a body of variable 

 elasticity ; with increased contraction its elastic force becomes 

 les?, its extensibility greater. When the muscle raises a given 

 weight about four millimetres, the external work for each milli- 

 metre of the lifting-height is indeed the.same but nevertheless the 



