January 5, 1922] 



NATURE 



15 



is not, therefore, the tension on the walls of the 

 heart which determines the strength of its contrac- 

 tion at its next beat. When, however, we come to 

 measure the volume of the heart, we find that in 

 the isolated heart this is directly proportioned to 

 the work which the heart has to accomplish. Thus 

 we find that the larger the heart — i.e. the more it 

 is dilated during diastole— the greater is the pres- 

 sure that it will get up at the sucx:eeding contraction 

 or systole. 



We may put this in another form, as is shown 

 by continuing our experiment over several hours, 

 \vhen we find that the worse the condition of the 

 heart muscle, the more it must dilate in order to 

 get up an adequate pressure. Other things remain- 

 ing equal, we thus see that the volume of the heart 

 during diastole is a measure of its physiological 

 condition, and we are not surprised that a failing 

 heart means a dilated heart. Of course there is a 

 limit to this power of adaptation. As the heart 

 dilates it is working at an ever-increasing me- 

 chanical disadvantage, and a point will finally 

 arrive at which this disadvantage more than counter- 

 balances the physiological effect of dilatation. The 

 heart then dilates widely and fails to empty its 

 contents. Dilatation of the heart means elongation 

 of the muscular fibres composing its walls, so that 

 we may put the law of the heart another way and 

 say that the longer its muscle fibres the greater is 

 the energy developed at each contraction. But in 

 this form this wonderful power of adaptation pos- 

 sessed by the heart becomes part of the general 

 properties of all muscular tissues, since the same 

 rule applies to the fibres composing our voluntary 

 muscles. Can we obtain any more precise and 

 physiological conception of what- is involved in this 

 relationship between length of fibre and strength of 

 contraction? Microscopic examination of the fibres, 

 either of the heart or of voluntary muscle, shows 

 that these are composed of innumerable fibrils, so 

 that internally the muscle is made up of structures 

 presenting an enormous extension of longitudinal 

 surfaces. The more the muscle is stretched, the 

 greater will be the extent of these surfaces. A large 



amount of evidence, based on the electrical and 

 chemical changes occurring in muscle as a result 

 of excitation, points to the contraction as being 

 essentially a surface phenomenon — a molecular 

 change over the whole of the longitudinal surface 

 which may result in a polarisation or depolarisation 

 of the surface and an increase of surface tension, 

 so that the muscle is a surface tension machine in 

 which there is on excitation a direct conversion of 

 chemical into surface energy. The greater the 

 surface the greater will be the number of molecules 

 involved, so that increased length of muscle must 

 increase at the same time the total chemical changes 

 and the total tension produced by the summation 

 of the surface tension of each fibril. 



It is only by such a change of molecular dimen- 

 sions that we can explain the rapidity of events in 

 a muscle (the insect wing muscle can contract and 

 relax 300 times per second), or the high efficiency 

 of the machine, an efficiency which A. V. Hill has 

 shown may amount to loo per cent, for each 

 isolated contraction, and over a length of time to 

 50 per cent. As directly measured in the heart- 

 lung preparation, we find a mechanical efficiency 

 of about 25-30 per cent. 



Conclusion. 



It is impossible here to enter into the applications 

 of this law of the heart, but so far it has not failed 

 in accounting for the behaviour of this organ under 

 all manner of conditions, either in health or disease. 

 It is important to remember, however, that we are 

 dealing here with the isolated heart. In the natural 

 body the mechanisms which we have studied are 

 fenced round, protected and aided by the complex 

 activity of the central nervous system, which is 

 always acting on the heart, balancing its activity 

 against that of the blood vessels, and co-ordinating 

 it with the events which are occurring in every other 

 part of the body. All these factors must be taken 

 into account when we are endeavouring to form a 

 conception of the total behaviour of this organ 

 under the varying activities of the intact animal. 



A Summer Visit to Jan Mayen Island. 

 By J. M. WoRDiE. 



TAN MAYP:N island lies in 71° N. latitude, 

 J 8-9° W. longitude, and is approximately 300 

 miles north of Iceland, 200 east of Greenland, and 

 600 west and north-west respectively of Tromso and 

 Aalesund — the leading hunting ports in Norway. It 

 was possibly discovered in 1607 by Henry Hudson 

 and named " Hudson's Tutches " ; the name, never- 

 theless, by which it is now known commemorates a 

 Dutch seaman, Jan Jacobsz May, who visited the 

 island in 16 14. The evidence for the earlier visit by 

 Hudson can scarcely be regarded as trustworthy. 

 May's voyage, on the other hand, is well supported 

 NO. 2723, VOL. 109] 



by documentary evidence. Immediately following 

 its discovery, Jan Mayen became frequented almost 

 every year by rival Dutch and British whalers. As 

 a whaling and sealing centre, however, the island 

 was markedly inferior to Spitsbergen. Its import- 

 ance was, nevertheless, far from small, and the 

 British Government is said to have made a grant of 

 it to the Corporation of Hull in 1618. The number 

 of whalers frequenting the island, however, dropped 

 off very considerably about 1635, the imme- 

 diate cause being probably a series of bad ice 

 vears. 



