THERMOGENETIC AND INOGENETIC PROCESSES. 399 



relation between the thermogenetic and biogenetic processes. In all 

 experiments in which it is desired to obtain quantitative results, the 

 muscle to be investigated is regarded as if it were a calorimeter. 

 Having placed it under such conditions as to prevent the transference 

 of heat to or from the surrounding media during the period of observa- 

 tion, the amount of heat produced during any thermogenetic process is 

 estimated by multiplying the increase of temperature by the weight of 

 the muscle, and the product by the specific heat of muscular substance. 

 Measurements of this kind are regarded as reliable, because it is found 

 that when the experiment is so made that the whole of the heat which 

 disappears in doing work can be measured, its relation to the quantity 

 of work done is in accordance with the first thermodynamic law. 



To prove this conformity, the amount of work done is measured in a series 

 of instantaneous excitations, following one another with such frequency as just 

 to allow the muscle to relax between each contraction and its successor. This 

 is done by a contrivance called, a "work-collector," consisting of a wheel around 

 the horizontal axle of which a cord supporting a weight is wound. Each time 

 the muscle contracts, it works on the periphery of the wheel so as to rotate it 

 and thereby lift the weight. As the wheel is prevented from moving back by 

 a catch, the weight is raised a little by each contraction, but never descends. 

 The total lifting work done in the series can thus be measured. The heat 

 produced during the series is measured at the same time. If H denotes the 

 heat value of the material oxidised, and Wh the heat equivalent of the 

 work done, H— Wh denotes the result of this measurement. To ascertain the 

 value of H the collector is dispensed with, and a second experiment is made, in 

 which the heat produced in the muscle is measured in an exactly similar series 

 of excitations, with the weight hung on to the muscle itself. In this case 

 the weight falls between each contraction and its successor, so that the heat 

 lost during contraction in doing external work is returned to the muscle 

 during relaxation. Consequently the amount of heat produced during this 

 series exceeds that measured in the first experiment by Wh, i.e., the equivalent 

 of the work done. If it were possible to make this experiment with perfect 

 exactitude, this difference, measured in microcalories, would be to the work 

 done, measured in gramme-millimetres, as 1 to 425. 



From experiments of this kind we learn what was the relation 

 between the quantity of material oxidised and the work done in any 

 particular case investigated. But no general inference can be drawn 

 from it as to the normal relation of material expended to work produced 

 in muscle, unless it is known that the conditions under which the 

 muscle worked were favourable, i.e., that they were such that the 

 amount of material used yielded the largest attainable result in work. 

 What these conditions are will be shown in the following paragraphs. 

 For the present purpose it is sufficient to say that for every muscle 

 there is a certain amount of load which cannot be either increased or 

 diminished without disadvantage, as regards the relation between the 

 work done and the material expended. If we seek to increase the work 

 done by increasing the load, we soon find that the effect of doing so is 

 more than made up for by the diminution of the lift, and similarly we 

 cannot increase the lift without finding the effect more than counter- 

 balanced by the diminution of the load. 



For the gastrocnemius of the frog such a load is about 200 grms. 

 When this is employed, the relation obtained between the heat- value of 

 the work done and that of the material used is about 1 to 4. In man 



