448 PRINCIPLES OF GENERAL PHYSIOLQC.Y 



at tin- critical point, and a negative coefficient is also found experimentally 

 (Freundlich, 1909, p. 32). In the paper by Bernstein s<>mc detttmmattODB of the 

 temperature coefficients of the surface tensions of colloidal solutions are given, and 

 shown to he negative (see also page 61 above). 



Mines (1913, 1, pp. 14-16) brings forward good reason for regarding the 

 production of lactic acid as responsible for the changes of surface energy, and shows 

 that, owing to there being an optimal hydrogen ion concentration for the contract ile 

 response, the first effect of the production may be an increase of this factor to 

 the optimal value; hence the phenomenon of the "staircase.'' Although the lactic 

 acid is rapidly removed, its disappearance cannot be instantaneous, and it will 

 probably attain a finite concentration in tetanus; at this concentration it will 

 be produced and removed at an equal rate. This concent rat ion is, no doubt, above 

 the optimal one, and hence the decrease in height of each succeeding twitch in the 

 summation of tetanus. These effects on excitability and tone are supposed by 

 Mines to be due to the diffusion of the lactic acid, first formed at the active 

 surfaces responsible for the production of the tension of the twitch. It will ! 

 noted, however, that we have, as yet, no explanation of the manner in which the 

 lactic acid is liberated by the stimulus, and why the process appears to be a 

 surface phenomenon. 



A further account of the question will be found in Macallurn's article (1911). 

 It seems clear that a sufficient change in tension might be obtained from surface 

 energy, but a decision on the point is not yet possible. In all probability, the 

 change of surface tension is the primary factor, but osmotic pressure may play 

 a part subsequently, although it seems somewhat doubtful whether sufficient 

 tension could be produced by this means alone, which acts rather at a disadvantage. 

 The movement of water, on the other hand, is most readily accounted for by 

 changes of osmotic pressure, but it may be merely incidental. 



Haber and Klemensicwicz (1909, p. 390), in their work on the force^ pie-cut 

 at the boundaries of phases, express the view of the intervention of surface tension 

 as follows : " The relation between the chemical process and the mechanical effect 

 of muscle is to be regarded in this way : production of acid alters the electrical 

 forces at the phase boundary ; this electrical change involves one of the surface 

 tension also, and it is this change of surface tension that brings about the 

 mechanical deformation of the muscle." 



With regard to several of the points discussed in the preceding pages, the 

 recent work of Weizsiicker (1914) gives important information. By means of a 

 method devised by A. V. Hill and himself (1914), experiments could be made on 

 the heat evolved by muscle immersed in various solutions. The "initial heat 

 production " is exactly the same with or without the presence of oxygen. It is 

 also unaffected when oxidation is prevented by potassium cyanide. With respect 

 to the action of this substance, the facts given in Chapter XX. may be referred 

 to. This part of the muscle process is, then, not an oxidation. It has been 

 mentioned above that the tension developed has a negative temperature coefficient, 

 and the same fact is shown by Weizsiicker to hold for the initial heat production. 

 Alcohol prevents the development of the tensile stress, while one-third or more 

 of the initial heat production remains. There are thus two parts or stages in the 

 contractile mechanism; namely, one part providing free energy, and another 

 which transforms this energy into mechanical potential energy or work. Both of 

 these are abolished, reversibly, by the use of hypotonic Ringer's solution, and at 

 the same time. The three different components of the act of contraction can tlms 

 be acted on. (1) Cyanide acts on the oxidations. (2) Temperature or hypotonic 

 saline on the initial liberation of energy. (3) Temperature or alcohol on the trans- 

 formation of this energy into the mechanical response. The oxidative recovery 

 process is affected by temperature in the same way as a chemical reaction. The 

 oxygen used increases, while the heat production falls, with a rise of temperature. 



The relaxation of tone in smooth muscle is another aspect of the negative 

 temperature coefficient of surface energy. 



Pauli (1912) has developed a theory on the lines of the colloidal chemistry of the compounds 

 of proteins with acid. I find it difficult to bring this view into connection with what we 



