272 CIRCULATION OF THE BLOOD. 



the liquid discharged by the sinus venosns must be constantly 

 replaced in the funnel ns it flows out. The work which is ex- 

 pended in doing this per minute is the work by which the cir- 

 culation is carried on. Thus, supposing the height of the 

 column of serum to be 400 millimetres, and that it is found 

 that the level of the liquid in the funnel begins to subside 

 when not supplied at such a rate that the weight of serum 

 flowing through the aorta during one second is equal to one- 

 fiftli of a gramme, then the force expended per second would 

 be that required to raise one-fifth of a gramme 400 millimetres, 

 i.e., one gramme to the height of a metre in 12.5 seconds, or 

 0.08 grammes to the same height in one second ; and this re- 

 sult has Ill-en arrived at in accordance with the proposition 

 with which we started, by multiplying the aortic pressure 

 (expressed in the height of a column of blood corresponding 

 to it) by the quantity discharged in the given time. 



If exact information were attainable as to the quantity 

 which the heart actually discharges at a stroke, it would be 

 possible to measure the quantity of work done by the heart in 

 the maintenance of the circulation in a mammalian animal, 

 and inferentially in man ; but inasmuch as no such method at 

 present exists, no estimate can be given which possesses even 

 approximate value. In the frog, however, a reliable estimate 

 can be made by the methods described in G3, whichever form 

 of experiment is employed. Thus, when the heart communi- 

 cates exclusively with the manometer, the work which the 

 heart is made to do is to raise whatever quantity of mercury 

 is contained in the manometer between the level at which it 

 stands during diastole and that to which it rises in systole, to 

 the mean height height , where h denotes the difference in 

 millimetres of the two levels. For evidently, of the whole 

 number of particles of mercury in the distal column, the sur- 

 face of which is caused to rise h millimetres above the surface 

 in the proximal column, it is only the top particles which are 

 raised // millimetres above the level of the proximal column ; 

 those in the exact middle are raised only half h ; those above 

 and below, less or more in proportion to their distance from 

 the middle ; so that the mean elevation is half h. The weight 

 is easily known if we know the aera, ?'. e., lumen, of the tube, 

 and the specific gravity of the mercury. If we designate the 

 former as a and the latter as s, we have the weight lifted by 

 the heart in each contraction to the height , expressed by a 

 x //, and the work done (that is, the product of the weight 

 lifted and the height to which it is lifted) ^ 2 . If it is desired 

 to obtain perfectly accurate results, a manometer must be used 

 of which the area of the surface of the mercury in the proximal 

 limb is relatively very large. In the other form of experiment, 

 64, i.e., when a continuous current of serum is pumped by 



