CHAPTER XXXIII 



CLINICAL APPLICATIONS OF CERTAIN PHYSIOLOGICAL 

 METHODS (Cont'd) 



THE MEASUREMENT OF THE MASS MOVEMENT OF THE BLOOD 



Method. The apparatus used for this purpose consists essentially of a vessel con- 

 taining a known quantity (3,000 c.c.) of water and a thermometer from which a change 

 of temperature of a hundredth of a degree centigrade can be read. In order to 

 diminish as much as possible the loss of heat between the vessel and the outside air, the 

 walls are double, the space between being stuffed with broken cork. The top of the 

 vessel is closed with a thick cork plate, having suitable openings in it for the hand or 

 foot and for the thermometer and a stirrer (feather) with which to keep the water in 

 constant motion. The apparatus is called a calorimeter. 



After the hand or foot has been in the calorimeter, with the water a few degrees 

 below that of the body, for a certain time (ten minutes) the temperature of the water 

 will of course become raised, and the degree to which this occurs, multiplied by the 

 volume of water in cubic centimeters, will give in calories the amount of heat dissipated. 

 By the application of a very simple formula it is now an easy matter to calculate how 

 much blood must have passed through the blood vessels of the part in order to give out 

 the observed amount of heat; for, if we divide the calories by the difference in tempera- 

 ture between the inflowing and outflowing blood of the part, the result must indicate 

 the volume of blood, in cubic centimeters, that has passed through it (since by defini- 

 tion a calorie equals volume multiplied by difference in temperature). It remains to 

 explain the equation by which the results are arrived at. If Q equals the amount of 

 blood, H the calories of heat given out to the calorimeter, T the temperature of the 

 arterial blood and T' the temperature of the venous blood, then we have the equation: 



H* 

 , , _. It has been shown by Stewart that T may be taken as the same as that 



of the mouth, or 0.5 C. below that of the rectum, and T' as the average temperature 

 of the water in the calorimeter during the observation. To allow for the specific heat 



of blood, the result is multiplied by IP, the reciprocal of the specific heat of blood. 



y 



Theoretically, then, the method is very simple, and there are no un- 

 usual technical difficulties in applying it. The main precaution is that 

 the air surrounding the calorimeter should be kept constant in tempera- 

 ture, so that we may be enabled to allow in our calculations for the loss 

 of heat from the calorimeter itself, this value being obtained by observ- 



*For the determination of H we must multiply the cubic centimeters of water plus the water 

 equivalent of the hand and calorimeter (because both of these will absorb some heat) by the dif- 

 ference in temperature plus the self-cooling of the calorimeter (because some heat is lost to the 

 air during the observation). The water equivalent of the hand is equal to its volume multiplied 

 by 0.8; that of the calorimeter must be determined for each instrument and is usually about 100 c.c. 

 The self-cooling of the calorimeter is determined by observing the fall in temperature for a period 

 equal to that of the actual observation without the hand in the calorimeter. 



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