306 THE EFFECTS OF FOOD. [BOOK i. 



augmentor system, and thus by increasing the work of the heart 

 raises or maintains the arterial pressure. 



On the other hand, we have reason to think that while that 

 part of the vaso-motor centre which governs the cutaneous vas- 

 cular area is being inhibited, that part which governs the abdominal 

 splanchnic area is on the contrary being augmented. In this 

 way a double end is gained. On the one hand, the mean blood 

 pressure is maintained or increased in a more economical manner 

 than by increasing the heart beats, and on the other hand, the 

 blood during the exercise is turned away from the digestive organs 

 which at the time are or ought to be at rest and therefore 

 requiring comparatively little blood. These organs certainly at 

 all events ought not during exercise to be engaged in the task of 

 digesting and absorbing food, and the old saying, " after dinner sit 

 awhile," may serve as an illustration of the working of the vascular 

 mechanism with which we are dealing. The duty which some of 

 the digestive organs have during exercise to carry out in the way 

 of excretion of metabolic waste products is as we have already 

 said probably taken on by the flushed and perspiring skin. It is 

 true that at the beginning of a period of exercise, before the skin 

 so to speak has settled down to its work, an increased flow of 

 urine, dependent on or accompanied by an increased flow of blood 

 through the kidney, may make its appearance ; but in this case, 

 as we shall see later on in dealing with the kidney, the flow of 

 blood through the kidney may be increased in spite of constriction 

 of the rest of the splanchnic area, and, besides, such an initial 

 increase of urine speedily gives way to a decrease. 



172. The effect of food on the vascular mechanism affords a 

 marked contrast to the effect of bodily labour. The most prominent 

 result is a widening of the whole abdominal vascular area, accom- 

 panied by so much constriction of the cutaneous vascular area 

 and so much increase of the heart's beat as are sufficient to neutra- 

 lize the tendency of the widening of the abdominal vascular area 

 to lower the mean pressure, or perhaps even sufficient to raise 

 slightly the mean pressure. 



The widening of the abdominal vascular area, as we have 

 seen ( 157), is probably an inhibition of tonic vaso-constrictor 

 impulses as a reflex act, assisted possibly by some local action 

 due to the presence of the food and similar to that supposed to 

 take place in the skeletal muscles during contraction. We 

 have at present no clear evidence that the absorbed products 

 of digestion play any important part in this splanchnic dilation by, 

 acting on the central nervous system ; but the concomitant 

 increase of the heart beat is probably due to this cause. We have 

 no exact knowledge of how the absorbed products bring this 

 about, and possibly the mode of action differs with the different 

 constituents of food. With regard to alcohol, which is so often 

 part of a meal, we may perhaps say that the character of its 



