CHAPTER XXXII 



CLINICAL APPLICATIONS OF CERTAIN PHYSIOLOGIC 

 METHODS (Cont'd) 



THE MEASUREMENT OF THE MASS MOVEMENT OF THE BLOOD 



Method. The apparatus used for this purpose consists essentially of 

 a vessel containing a known quantity (3,000 c.c.) of water and a ther- 

 mometer from which a change of temperature of a hundredth of a de- 

 gree 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 the 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 temperature between the inflowing and out- 

 flowing blood of the part, the result must indicate the volume of blood, in 

 cubic centimeters, that has passed through it (since by definition 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 



H* 



venous blood, then we have the equation : Q= 7^7. It has been shown 



*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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