BLOOD FLOW IN MAN. 213 



wet, in water which completely fills a lipped thick-walled beaker of 

 suitable size. The hand displaces an equal volume of water, which 

 overflows into a basin in which the beaker is standing. When no 

 more water overflows, the hand is slowly withdrawn, and water 

 is added from a graduate to the beaker until it is again full; the 

 amount of water required gives the volume of the hand. 



The temperature of the mouth or rectum is finally taken and 

 the temperature of the room, read from a thermometer hanging 

 from the chair on which the subject sits, recorded. 



To apply the above formula to calculate the blood flow it is necessary to 

 introduce several corrections to allow for differences in the specific heats of the 

 hand tissues, of the metal of the calorimeter and of water. These corrections are 

 expressed as the water equivalents of the hand and calorimeter. The water 

 equivalent of the calorimeter is determined experimentally for each calorimeter,, 

 and for one of the above dimensions will be about 100 c.c. The water equivalent 

 of the hand is obtained by multiplying its volume by 0.8, this factor being the 

 product of the specific gravity and the specific heat of the hand. 



Suppose in an experiment that the temperature of the calorimeter during an 

 observation lasting 10 minutes had risen from 31 C to 31.5 C and the self-cooling 

 of the calorimeter during the subsequent 10 minutes was 0.1 C, the mouth 

 temperature being 37.5 C. and the volume of the hand 450 c.c., then (applying 

 the above equation) : 



(3000+100+360)c.c.X(0.5+0.1)C 10*_ 



37.5-31.25f ( 9 = 



The measurement should now be repeated under the following 

 conditions: 



1. When the opposite hand, instead of being carefully pro- 

 tected from cooling, is placed in cold water. A marked curtail- 

 ment of blood flow, due to reflex vaso-constriction, will be observed. 

 This observation may be made in continuation of the previous one, 

 i.e., the unobserved hand kept covered for 10 minutes and then 

 placed in cold water for the next 10 minutes. It is particularly 

 important in these observations to read the calorimeter temperature 

 at frequent intervals, because the vaso-constriction that is im- 

 mediately induced gives place later to a dilatation, even while 

 the opposite hand is still in the cold water. The blood-flow result 



*This is the reciprocal of the specific heat of blood. 



fThis is the mean temperature in the calorimeter during the observation 



(36 9) 

 of the hand --- - -8.2 



