CHAPTER XXVIII. 



MEASUREMENT OF THE BLOOD FLOW THROUGH THE 

 HANDS AND FEET, BY THE CALORIMETRIC 

 METHOD OF G. N. STEWART. 



ELECTROCARDIOGRAPHY 



Because of their relatively great exposed surfaces the hands, 

 and to a lesser degree the feet, quickly give off heat to their en- 

 vironment. They are excellent radiators. The muscles of these 

 parts when at perfect rest, contribute but a very small quota to 

 this heat, most of which therefore is carried to them by the blood 

 from other parts of the body. From these considerations it follows 

 that the amount of heat given out in a given time must be pro- 

 portional to the amount of blood flow, or expressed in precise 

 terms: the amount of heat given off in calories, divided by the 

 difference in temperature between the blood flowing to and away 

 from the part equals the volume flow of blood in cubic centimetres.* 



If Q be the grammes of blood per minute, H the gram calories 

 in m minutes, T the temperature of the blood entering the hand and 

 T' that of the blood leaving it, S being the specific heat of blood then : 



_ H 1 



Q== m(T-T') T" 



The calories are measured by placing the hand in a water 

 calorimeter; the temperature of the entering blood may be taken, 

 as that under the tonguef and the temperature of the leaving 

 blood T', as the mean temperature of the calorimeter during the 

 observation. 



The calorimeter (see Fig. 64) consists of a tinned inner copper vessel capable 

 of holding somewhat over 3000 c.c. of water. This vessel is placed within a wider 

 vessel, the space between the two being packed with broken cork. To the open 

 upper end of the inner vessel is soldered a lid of copper with a hole cut in it 

 towards one side of the centre and large enough and shaped so as to allow the 



*A small or gram calorie is the amount of heat required to raise the tempera- 

 ture of 1 gm. of water through 1 C. 



fBecause of the liability of the mouth temperature to vary, it is more accurate 

 to take for T the rectal temperature less 0.5 C. 



210 



