166 



A TEXTBOOK OF PHYSIOLOGY 



throwing up a 5-ounce ball a yard high seventy times a minute. The 

 right ventricle, since it contracts against considerably less pressure, 

 has less work to do. It is generally considered as doing about one- 

 third the work of the left. 



Taking into consideration the variations in pressure and output, 

 the human heart is estimated to perform about 12,000 to 20,000 kilo- 

 gramme-metres of work per day that is to say, it performs sufficient 

 work to raise the body weight through 200 to 300 metres above sea- 

 level say up a hill of 1,000 feet. 



Twenty thousand kilogramme-metres would be equivalent to 50 

 calories out of the total 3,000 calories which a man takes in as food. 

 A labourer does about 150,000 kilogramme-metres of external work a 

 day. The work of the heart is increased two or three times by muscular 

 labour, and even ten times by great exertion. When the heart does 

 work it also produces heat, and probably five times as much heat as 

 work. It has been estimated that the heart requires per diem, to 



Recorder 

 FIG. 68. THE CARDIOMETER. 



maintain its energy, an amount of solid food (water -free) equal to the 

 weight of solids in the heart itself i.e., about 60 grammes of sugar 

 or protein. A relatively high proportion of blood must be circulated 

 per minute through the coronary arteries to maintain the vigour of 

 the heart, and its use of oxygen per gramme of weight per minute is 

 high. Thus, for the whole body of the dog there was used 0-017 c.c. 

 per gramme of tissue per minute; for the heart, 0-045 to 0-083; and 

 for the active secretory glands, 0-07 to 1-0. 



The volume of the output of the heart may be recorded by means 

 of the cardiometer. 



Various forms have been devised. The most convenient consists 

 of a large thistle funnel covered with a rubber membrane in which 

 a round hole of appropriate size has been made with a heated soldering- 

 iron (Fig. 68). After the establishment of artificial respiration, the 

 thorax of the animal is opened and its heart inserted through the rubber 

 membrane so that this fits snugly to the base of the ventricles. The 

 tube of the funnel is connected with a piston recorder. A canmila 



