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SCIENCE 



[N. S. Vol. XLII. No. 1085 



ing for the electromotive changes in cells 

 is practically the same as that given by 

 Bernstein. 



It wiU be found of interest to apply to 

 secretory cells the facts to which I have 

 directed your attention. If we suppose 

 that the setting into play of such cells is 

 associated with the production of some 

 osmotically active substance, together with 

 abolition of the state of semi-permeability 

 of the membrane covering the ends of the 

 cells in relation with the lumen of the 

 alveolus of the gland, it is plain that water 

 would be taken up from the lymph spaces 

 and capillaries and escape to the duct, 

 carrying with it the secretory products of 

 the cells. This process would be continuous 

 so long as osmotically active substances were 

 formed. Such a process has been shown by 

 Lepeshkin to occur in plants, and we have 

 also evidence of increased permeability 

 during secretory activity in the gland cells 

 of animals. From what has been said pre- 

 viously, it is evident that electrical differ- 

 ences would show themselves between the 

 permeable and semipermeable ends of such 

 cells, as has been found to be the case. 



As a modifiable structure, we see the im- 

 portance of such a membrane as that de- 

 scribed if it takes part in the formation of 

 the synapse between neurones. The mani- 

 fold possibilities of allowing passage to 

 states of excitation or inhibition and of 

 being affected by drugs wiH be obvious 

 without further elaboration on my part. 



Enough has already been said, I think, 

 to show the innumerable ways in which 

 phenomena at phase boundaries intervene 

 in physiological events. Indeed, there are 

 very few of these, if any, in which some 

 component or other is not controlled by the 

 action of surfaces of contact. But there is 

 one especially important case to which I 

 may be allowed to devote a few words in 

 conclusion. I refer to the contractile proc- 



ess of muscle. It has become clear, chiefly 

 through the work of Fletcher, Hopkins 

 and A. V. Hill, that what is usually called 

 muscular contraction consists of two parts. 

 Starting from the resting muscle, we find 

 that it must have a store of potential energy, 

 since we can make it do work when stimu- 

 lated. After being used in this way, the 

 store must be replenished, since energy can 

 not be obtained from nothing. This res- 

 toration process is effected by an inde- 

 pendent oxidation reaction, in which car- 

 bohydrate is burnt up with the setting free 

 of energy which is made use of to restore 

 the muscle to its original state. Confining 

 our attention for the moment to the initial, 

 contractile, stage, the essential fact is the 

 production of a certain amount of energy 

 of tension, which can either be used for the 

 performance of external work or be allowed 

 to become degraded to heat in the muscle 

 itself. It was Blix who first propounded 

 the view that the amount of this energy of 

 tension is related to the magnitude of cer- 

 tain surfaces in the muscle fibers. But the 

 fact was demonstrated in a systematic and 

 quantitative manner by A. V. Hill. He 

 showed, in fact, that the amount of energy 

 set free in the contractile process is directly 

 related to the length of muscle fibers dur- 

 ing the development of the state of tension. 

 In other words, the process is a surface phe- 

 nomenon, not one of volume, and is directly 

 proportional to the area of certain surfaces 

 arranged longitudinally in the muscle. 

 This same relationship has been shown by 

 Patterson and Starling to hold for the 

 ventricular contraction of the mammalian 

 heart and by Kosawa .for that of the cold- 

 blooded vertebrate. It appears that all the 

 phenomena connected with the output of 

 blood by the heart can be satisfactorily ex- 

 plained by the hypothesis that the energy 

 of the contraction is regulated by the length 

 of the ventricular fibers during the period 



