PRACTICAL EXERCISES 221 



volume of hand, 450 c.c.; rectal temperature, 37'o C.; water equivalent 

 of calorimeter, 100 c.c. 



The water equivalent of the hand is 450 x o - 8*= 360 c.c. 

 The water equivalent of the calorimeter is - 100 c.c. 

 Water - - 3,000 c.c. 



Total - - 3,460 c.c. 



3,46ox n = 3,8o6 small calories given off by the hand in twenty 

 minutes. 



Temperature of arterial blood (36' 5) minus temperature of venous 

 blood (31*5*, the mean temperature of the calorimeter) = 5*0. 



3,806 lot 

 Flow per minute through hand=- x ' =42*3 grm. 



20 x 5 9 

 Flow per 100 c.c. of hand per minute = 9' 4 grm. 



The readings of the calorimeter thermometers for the first one or two 

 minutes may not be usable, owing to disturbance caused by the intro- 

 duction of the hands. As soon as they begin to rise steadily and 

 uniformly, the readings can be utilized for the calculation of the flow. 



32. Vasomotor Reflexes. Begin as in 31,, Then, after the hands 

 have been in the calorimeters for a sufficient period (say ten minutes) to 

 allow satisfactory readings for the determination of the blood-flow to 

 be obtained, rapidly transfer one hand to cold water (at about 8 C.), 

 while the other remains in the calorimeter. Continue reading the 

 calorimeter thermometer. Its rise will be checked by reflex vaso- 

 constriction. If the hand is kept for a few minutes in the calorimeter, 

 the reflex vaso-constriction of the hand in the calorimeter will probably 

 disappear, and the thermometer will rise faster. When a sufficient 

 number of readings have been obtained for calculating the alteration 

 in the flow, which will usually be the case in eight or ten minutes, 

 transfer the hand from the cold water to warm water (at about 43 C.), 

 and continue reading the calorimeter thermometer. There is usually 

 a reflex vaso-constriction followed by vaso-dilatation. 



* This factor is the product of the specific gravity and the specific heat of 

 the hand. The volume multiplied by the specific gravity gives the mass of 

 the hand, which multiplied by the specific heat, gives the water equivalent of 

 the hand. 



t The reciprocal of the specific heat of blood (see formula, p. 122). 



