January 5, 1922] 



NATURE 



13 



The Law of the Heart.' 



By Prof. E. H. Starling, C.M.G., F.R.S. 



THE discovery by Harvey of the circulation of 

 the blood, and of the part played by the heart 

 in carrying on this circulation, is one of the few 

 scientific discoveries which have become common 

 knowledge. We have to think of the body as a 

 collection of mechanisms or machines, each one of 

 which is doing some form of work for one common 

 end — i.e. the preservation of the body. For this 

 work the oxidation of the food taken in at intervals 

 during the day provides the energy ; thus each part 

 of the body must be supplied not only with food 

 derived from the alimentary canal, but also with 

 the oxygen taken in with the air we breathe into 

 the lungs. Like any other machine, each body 

 mechanism produces, as a result of this consumption 

 of the food, waste gases and other waste products 

 which have to be carried to the lungs or to the 

 kidneys and there cleared out of the body. It is 

 for this reason that the existence of the higher 

 animal demands a common fluid, the blood, which 

 can carry food, oxygen or carbonic acid, and 

 is maintained in continual circulation between all 

 the organs of the body, so that the alimentary canal, 

 for instance, may serve for the maintenance of all 

 parts, and the lungs can supply oxygen to these 

 parts or excrete the carbonic acid which is produced 

 as a result of their activity. 



But a uniform mechanical circulation Avould be of 

 little value to the body, since the activities of all 

 its parts vary within wide limits. Thus, during 

 muscular exercise the activity of the muscles may 

 Ije increased tenfold or more, and this increase 

 means a corresponding augmentation in their call 

 for oxygen and in the quantity of waste products, 

 especially carbonic acid, that they produce. Since 

 the oxygen is carried by the blood, it follows that 

 for the continued functioning of the muscles these 

 must receive a blood supply which is ten times 

 eater during activity than during rest if their 

 ,,^tivity is not to be brought to an end by a species 

 suffocation. Therefore, in any violent exercise in- 

 lying the greater number of the muscles of the 

 'ly, the circulation must be increased in force 

 _ ;n to ten times, and the heart, which is the pump 

 [intaining the circulation, must under these con- 

 do from seven to ten times as much work as 

 ring rest. 



The Mechanism of Adaptation. 

 'hat is the mechanism of these adaptations? 

 How is it that the heart is able to carry on a circula- 

 tion which may vary from a passage of 3 litres of 

 blood per minute up to 30 litres of blood per 

 minute (these figures representing the extreme limits 

 between which the output of the heart-pump may 

 vary according to the condition of the body)? It 

 might be thought that we are dealing here simply 

 with the influence of the central nervous system, 



» Discorrse delivered at the Royal Institution on Friday, May 20, 1921. 



NO. 2723, VOL. 109] 



which adapts the activity of the muscles of the body 

 ' to the requirements of the environment, and that the 

 ' heart being a muscle would be stimulated to con- 

 tract more strongly at the same time as the nervous 

 system calls into activity the voluntary muscles of 

 j the body. There is no doubt that the heart is 

 under the control of the central nervous system, so 

 that its action can be altered, increased, or dimin- 

 I ished by the brain in accordance with the needs of 

 '< the economy, but in the heart we find also a won- 

 derful power of adaptation to the varying require- 

 ! ments of the organism which is quite independent 

 : of the central nervous system. 



i This can be shown quite easily either in the cold- 

 I blooded or warm-blooded animal. The heart of the 

 frog and tortoise can be cut out and will continue 

 beating for hours or even days. It has long been 

 ' known that the heart of the mammal would beat 

 ; for some minutes after being cut out of the body, 

 ; but if we take pains to ensure that the muscles con- 

 [ stituting the walls of the heart continue to receive 

 i their supply of oxygenated blood, the mammalian 

 I heart can be made to beat for eight to twelve hours 

 i after the death of the animal from which it is taken. 

 j In order to investigate this properly we want to 

 i make such a preparation that we can control at will 

 I all the conditions which may affect the action of the 

 , heart — viz. the amount of blood flowing into the 

 heart from the big veins, the resistance which the 

 heart has to overcome when it drives the blood out 

 into the arteries, and the temperature at which the 

 heart contracts. We must be able to measure at 

 any time the output of the heart, the arterial pres- 

 sure it maintains, its changes in volume during con- 

 traction, the pressure in all its cavities during con- 

 traction, the amount of blood flowing through the 

 blood vessels of its walls, and its chemical ex- 

 changes, as measured by the amount of oxygen 

 which it takes up and the amount of carbonic acid 

 which it produces. It is these chemical changes 

 which give the energy for the work of the heart. 



The Heart-Lung Preparation. 



All these procedures and controls can be carried 



\ out in the heart-lung preparation. In this prepara- 



I tion the pulmonary circulation from right ventricle 



to left auricle is left intact, and by means of arti- 



1 ficial respiration the lungs are blown up rhythmic- 



! ally so that the blood in its course may take up 



; oxygen and get rid of carbonic acid. The whole 



i systemic circulation is replaced by rubber tubes. A 



' glass tube is tied into the largest branch of the 



1 aorta, all the other branches being tied, so that the 



' blood driven out by the left ventricle can escape 



only by the glass tube. From the glass tube a 



rubber tube passes to a thin rubber tube container 



within a wide glass tube. This thin rubber, tube 



can be compressed to any desired extent by pumping 



air at a known pressure intr» the £;1a«> tube 



