Answer
The fainting of the tuba player could may have one of several related etiologies (causes).
1. Some people have a condition that causes them to faint if they play a brass instrument. This is not likely to be the case here. But Harvey could have been suffering from dehydration. It was a hot day and he was wearing a heavy warm uniform. His body would have tried to move blood from core to shell to enhance body cooling and maintain heat homeostasis. However, if he was not well hydrated he might have lost too much blood volume by perspiration, and had not enough volume left to adequately supply his brain. In such a case, the brain takes no chances it sends messages to skeletal muscles and somatic nerves to cease functioning and the subject (Harry) collapses. Once Harry is prone and the blood return is no longer fighting the pull of gravity, the brain receives enough blood, oxygen, and glucose. Harry will be fine as long as he stays horizontal-- or seated-- until he replenishes his blood volume and his normal blood pressure returns.
The classical case of syncope (fainting) of soldiers and bandsmen happens when either has to stand at attention for too long a time. Some members of these groups will "lock" their knees to remain upright if they get tired of standing and need some kind of support. However, this causes blood to pool in there leg veins. Venous pressure is not high and venous return depends to a large extent on muscle movement, especially skeletal muscle movement. If Harry was standing immovably still for a long time, the unbroken columns of venous blood would not have enough muscle pump pressure exerted on them to get enough back up to adequately supply the brain with oxygen and glucose. The brain does not store either of these essentials ( glucose and oxygen), so when the supplies cease coming, and it feels endangered, it signals the skeletal muscles and nervous system to quit. Then the band member or soldier falls, and blood flows once again to the brain; as a result the fainter revives. In Harry's case, both dehydration and gravity might have combined to do him in, temporarily, but ultimately to save him.
Work Step by Step
Harry's syncope may have been due to a combination of dehydration and pooling of blood in leg veins. This condition developed because of lack of muscular movements to get enough blood back to his brain against the pull of gravity. In such a case, the brain is very selfish, and shuts down until it gets essential supplies. When this happens the subject faints.
