A "HEAD OF PRESSURE" 117 



be impossible, as Dr Leonard Hill has shown, to regulate 

 the distribution of blood to the various parts of the body. 

 Everyone knows how difficult it is to do head work im- 

 mediately after a meal. The stomach and organs of 

 digestion have then their vascular stopcocks turned full 

 on ; the needs of the stomach take precedence then to 

 those of the brain. The brain, if it pushes hard enough, 

 may obtain a blood-supply at the expense of that rightfully 

 designated for the organs of digestion, but it' is certain 

 to have to pay for its greed sooner or later by headache. 

 Every time we alter our posture — when we tie down, 

 stand up, or sit upright — there is a silent and automatic 

 switching of the tens of thousands of vascular stopcocks 

 of the body. We are so unconscious of this silent 

 activity that we find it difficult to believe that it actually 

 occurs. A moment's reflection will show that this 

 switching on and ofF must take place. When we rise 

 from bed in the morning our feet and legs, were it not 

 for the automatic turn-cocks, would draw all the blood 

 from the head, for they have the advantage of gravity. 

 Our hands would be engorged, while our shoulders would 

 starve for blood ; the organs in the upper part of the 

 body would bleed into those in the lower part. The 

 moment we stand up the vascular controlling centres in 

 the spinal cord — being nerve exchange centres, receiving 

 and giving thousands of messages of which we are un- 

 conscious — come into action and regulate the distribution 

 of blood by turning ofF and on the vascular stopcocks 

 of the body. This machinery may break down under 

 certain circumstances, particularly after we have been kept 

 standing in a hot stuffy room in a crowd of people. We 

 may then have a sudden faint and collapse on the floor, 

 because the vascular stopcock machinery has been over- 

 taxed or broken down. The blood has been drained 

 from the brain ; hence the unconsciousness. 



There is another wonderful mechanism brought into 

 operation by the animal machine when an effort has to be 

 made — a mechanism made clear to us in late years by 

 Professor W, B. Cannon of Harvard University. It 



