ENERGETICS 



43 



metabolism is directly proportional to the increase of rate, so that we have again a 

 linear relation. It will be plain that, in such a case as that before us, one cannot 

 speak of a " coefficient " in the strict sense. If such a number be calculated for 

 any particular temperature, it will not apply to any other temperature. 



Consider indeed, for a moment, the complexity and variety of the forms of 

 energy change involved in a muscular contraction surface and volume energy, 

 thermal, electrical and chemical energy. I think that it must be admitted 

 that to attempt to draw conclusions from the temperature coefficient of the 

 entire process does not seem likely to lead to results of much value. This 

 remark, of course, applies to the activities of living protoplasm in general, as 

 well as to muscle. 



2t>C 



HO" 



Krogh (1914, 1), more- 

 over, finds that the velocity 

 of embryonic division in 

 amphibia, fish, insects, and 

 echinoderms cannot, even 

 approximately, be ex- 

 pressed by the van't Hotf 

 formula of temperature 

 effect on chemical reac- 

 tions. Between normal 

 limits, the relation is a 

 linear one. In a further 

 paper (1814, 2), Krogh finds 

 that there is no optimum 

 temperature for the evolu- 

 tion of carbon dioxide, 

 and that this process also 

 follows a linear law. 



Regarded from an- 

 other point of view, we 

 must remember that 

 these vital phenomena 

 are taking place in 

 heterogeneous systems, 

 that is, in systems con- 

 sisting of various solid 

 and liquid phases. 

 When not coarsely 

 heterogeneous, they 

 are, at least, colloidal, 

 or ultra microscopically 

 heterogeneous. We 

 have, therefore, several 

 processes in addition 

 to the purely chemical 



one going on together, viz., diffusion of constituents of the reaction to and from 

 the surface where the reaction occurs, similarly to the action of hydrochloric acid 

 on a plate of marble, followed by condensation on the surface and so forth. As 

 Nernst points out (1911, p. 587), the velocity of the process as a whole will 

 be conditioned by tha.t factor which takes place at the slowest rate. In many 

 cases this is diffusion, as in the experiments of Brunner (1904, p. 56). But it 

 does not seem necessary that this should always be the case. It is con- 

 ceivable that the chemical factor in the complex may be slowed down, as by 

 a low temperature, so far as to become slower than the diffusion factor. In 

 such a case, the "limiting factor," to use Blackman's expression, would be 

 transferred from the diffusion process to the chemical reaction. I am not 

 aware, however, that any instance of such a change has been met with. 



Further discussion of heterogeneous reactions will be found in Chapter X. , when treating 

 of catalytic action. In the present place, attention is directed mainly to the complexity of 

 any given vital process, and to the uncertainty as to what factor is the controlling one in the 

 velocity of the reaction, or which one it is whose temperature coefficient is being measured. 



FIG. 28. EFFECT OF TEMPERATURE ON THE RATE OF THE 

 BEAT OF THE ISOLATED MAMMALIAN HEART. 



Abscissae temperature. 



Ordinates number of beats per minute. 



Between the limits of 26 and 40, in which the heart continues to con- 

 tract normally, the relation is linear. There is no temperature 

 " coefficient." 



(Knowlton and Starling, 1912, p. 217.) 



