MECHANICS OF THE CIRCULATION IN THE VESSELS 127 



possible that such habitual differences are associated with differences 

 in the total heat value of the food consumed or in the proportions of 

 the various food substances, especially of proteins (see p. 605), 

 for it is well known that even persons engaged in the same work, and 

 living under similar external conditions, may differ greatly in their 

 dietetic habits, both as to quantity and quality of the food. And since 

 the cutaneous circulation is by far the most important factor in the 

 loss of heat from the body, the hearty eaters, other things being equal, 

 may be expected to have the largest blood-flow through parts like the 

 hands. The importance of the flow through the skin in the total hand 

 flow is illustrated by the fact that the flow per unit of volume through 

 the distal half of the hand, which, of course, has a large surface in 

 proportion to its volume, is considerably greater than through the hand 

 as a whole. For the forearm the flow per 100 c.c. is, in its turn, much 

 less than in the hand (Hewlett) . In the foot the blood-flow, as estimated 

 by the calorimetric method, is smaller per unit of volume of the part 

 than in the hand, the ratio of foot flow to hand flow per 100 c.c. of the 

 part usually lying in normal persons between i to 3 and i to 2. This 

 is largely due to the proportionally greater proportion of skin in the 

 hand, as well as to the smaller proportion of bone, which has not an 

 active circulation. In the sitting position the following results were 

 obtained for the flow in the feet on the person whose hand flows have 

 been given above : 



The great variations in the vascularity of different organs and parts, 

 as revealed by the examination of injected specimens or by inspection 

 of the organs during life, indicate that there must be great differences 

 in the blood-flow. Observations with the stromuhr in animals have 

 shown that this is the case. The following list gives the number of 

 c.c. of blood passing per minute through 100 grammes of organ, according 

 to the results of Burton-Opitz, Tigerstedt, and other observers : 



Posterior extremity. 5 Liver (venous) . 59 



Skeletal muscle . 12 Liver (total) . . .84 



Head .... 20 Brain . . ... . 136 



Stomach .. 21 Kidney .. . 150 



Liver (arterial) > 25 Adrenal . . . 500 



Intestines . . 31 Thyroid gland . 560 



Spleen .. 58 



The Volume-Pulse. When the pulse-wave reaches a part it dis- 

 tends its arteries, increases its volume, and gives" rise to what may 

 be called the volume-pulse. 



